Announcement

**Pathfinder** · March 22, 2019, 04:00 PM

FluWatch report: March 10, 2019 to March 16, 2019 (week 11)

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Organization: Public Health Agency of Canada
Date published: 2019-03-22

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Overall Summary

Influenza activity continues to be reported in almost all regions in Canada but is circulating at higher levels in eastern regions.
Detections of influenza A(H3N2) have been steadily increasing since mid-January and accounted for 64% of subtyped influenza A detections this week; however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season.
There is currently very little influenza B circulation compared to previous seasons.
The World Health Organization (WHO) has released the recommended composition of the influenza vaccine for use in the 2019-2020 northern hemisphere influenza season. The recommended strain was changed for each of the A(H1N1)pdm09 and A(H3N2) components compared to this year's vaccine.

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Influenza/ILI Activity (geographic spread)

During week 11, the following influenza activity levels were reported (Figure 1):

19 regions reported localized activity: in Alta.(2), Man.(1), Ont.(6), Que.(3), N.S.(4), N.B.(1), and N.L.(2).
29 regions reported sporadic activity: in B.C.(5), Alta.(3), Man.(2), Ont.(1), Que.(3), N.B.(6), N.L.(2), P.E.I.(1), Nvt.(1), Y.T.(1) and N.W.T.(1)
Five regions: in Man.(2), Nvt.(2) and N.W.T.(1) reported no activity.

Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-11

Figure 1 - Text equivalent Laboratory-Confirmed Influenza Detections

In week 11, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

The percentage of tests positive for influenza continued to increase slightly to 21.4%.
A total 1,721 laboratory detections of influenza were reported, of which 95% were influenza A.
Influenza A(H3N2) accounted for 64% of subtyped influenza A detections.
Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 339 this week.

To date this season, 37,610 laboratory-confirmed influenza detections have been reported:

98% have been influenza A.
Among the 12,926 influenza A viruses subtyped, 83% have been A(H1N1)pdm09.
Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 29,558 laboratory-confirmed influenza cases (Table 1):

84% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
59% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-11

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Figure 2 - Text equivalent Figure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-11

Figure 3 - Text equivalent

0-4	5965	1632	91	4242	95	6060	21%
5-19	4255	1348	175	2732	134	4389	15%
20-44	5709	1845	268	3596	98	5807	20%
45-64	5722	1774	236	3712	67	5789	20%
65+	7344	1288	1097	4959	169	7513	25%
Total	28995	7887	1867	19241	563	29558	100%
Table 1 - Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 - Note1

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 11, 0.7% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4). The percentage of visits for ILI is low compared to previous seasons.
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-11

Number of Sentinels Reporting in Week 11: 75

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-14 to 2017-18
Figure 4 - Text equivalent Participatory Syndromic Surveillance

In week 11, 2,066 participants reported to FluWatchers, of which 54 (2.7%) reported symptoms of cough and fever (Figure 5).
Among the 54 participants who reported fever and cough:

13% consulted a healthcare professional;
75% reported days missed from work or school, resulting in a combined total of 124 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-11

Number of Participants Reporting in Week 11: 2,066

Figure 5 - Text equivalent Influenza Outbreak Surveillance

In week 11, 29 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (16), acute care facilities (2) and other settings (11). Two new ILI outbreaks (one in a school and one in a LTCF) were also reported in week 11.
To date this season, 586 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

346 (59%) outbreaks were in LTCF, 29 were in schools, 86 in acute care facilities, and 125 were in other settings.
Among the 523 outbreaks for which the influenza type was available, 98% (512) were associated with influenza A.
Among the 221 outbreaks for which the influenza A subtype was available, 55% (121) were associated with influenza A(H1N1)pdm09;

To date this season, 121 ILI outbreaks have been reported; 65 occurred in LTCF, 52 in schools, and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-11

Figure 6 - Text equivalent Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 2,474 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1.
Hospitalizations (Table 2):

99.0% (2,449) were associated with influenza A
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 446 ICU admissions and 109 deaths have been reported.
- 42% (189) of reported ICU admissions were in adults aged 45-64 years.
- All but four ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	343	9	73.95
5-19	204	8	15.28
20-44	311	1	10.97
45-64	670	2	30.88
65+	921	5	76.11
Total	2449	25
%	99.0%	1.0%
Table 2 - Note 1 Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 - Note1

Pediatric Influenza Hospitalizations and Deaths

In week 11, 37 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7).
To date this season, 1,046 pediatric hospitalizations have been reported (Figure 8):

67% of cases were in children under 5 years of age.
97% (1,017) of cases have been associated with influenza A.
Among the 316 cases for which the influenza subtype was available, 286 (91%) were associated with A(H1N1)pdm09.

To date this season, 188 ICU admissions, and 10 deaths have been reported.

61% (114) of ICU admissions were in children under 5 years of age.
All but two of the ICU admissions have been associated with influenza A.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-11

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Figure 7 - Text equivalent Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-11

Figure 8 - Text equivalent Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 729 hospitalizations, 88 ICU admissions and 32 deaths have been reported (Figure 9):

676 (93%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
86% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 82% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-11

Figure 9 - Text equivalent Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,622 influenza viruses (212 A(H3N2), 1,375 A(H1N1) and 35 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

102 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

17 viruses belonged to genetic group 3C.2a.
82 viruses belonged to subclade 3C.2a1.
Two viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

74 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
27 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
53 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 16 viruses belonged to genetic group 3C.2a and 21 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,336 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
39 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

Nine influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
Seven viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
19 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.
...

https://www.canada.ca/en/public-heal...h-16-2019.html

**Pathfinder** · March 30, 2019, 10:43 AM

FluWatch report: March 17, 2019 to March 23, 2019 (week 12)

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Organization: Public Health Agency of Canada
Date published: 2019-03-29

Related Topics

Overall Summary

Influenza activity continues to be reported in almost all regions in Canada but is circulating at higher levels in some eastern regions.
Though A(H1N1) peaked at end of December, over the past four weeks a second smaller wave, dominated by A(H3N2), is being observed in most regions of the country.
Detections of influenza A(H3N2) have been steadily increasing since mid-January and accounted for 72% of subtyped influenza A detections this week; however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season.
Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.

On this page

Influenza/Influenza-like Illness Activity (geographic spread)

During week 12, the following influenza activity levels were reported (Figure 1):

15 regions reported localized activity: in Alta.(1), Ont.(6), N.S.(3), N.B.(2), P.E.I.(1) and N.L.(2).
33 regions reported sporadic activity: in B.C.(5), Alta.(4), Sask.(3), Man.(4), Ont.(1), Que.(6), N.B.(5), N.L.(2), N.S.(1), Y.T.(1) and Nvt.(1)
Three regions: in Man.(1) and Nvt.(2) reported no activity.

Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-12

Figure 1 - Text equivalent Laboratory-Confirmed Influenza Detections

In week 12, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

The percentage of tests positive for influenza continued to increase slightly to 21.8%.
A total 1,735 laboratory detections of influenza were reported, of which 93% were influenza A.
Influenza A(H3N2) accounted for 72% of subtyped influenza A detections.
Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 342 this week.

To date this season, 39,297 laboratory-confirmed influenza detections have been reported:

98% have been influenza A.
Among the 13,414 influenza A viruses subtyped, 81% have been A(H1N1)pdm09.
Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 30,844 laboratory-confirmed influenza cases (Table 1):

84% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
57% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-12

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Figure 2 - Text equivalent Figure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-12

Figure 3 - Text equivalent

0-4	6093	1639	106	4348	115	6208	20%
5-19	4425	1359	240	2826	176	4601	15%
20-44	5905	1882	298	3725	117	6022	20%
45-64	5915	1800	292	3823	70	5985	19%
65+	7852	1320	1265	5267	176	8028	26%
Total	30190	8000	2201	19989	654	30844	100%
Table 1 - Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 - Note1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 12, 1.6% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-12

Number of Sentinels Reporting in Week 12: 86
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-14 to 2017-18
Figure 4 - Text equivalent Participatory Syndromic Surveillance

In week 12, 2,056 participants reported to FluWatchers, of which 50 (2.4%) reported symptoms of cough and fever (Figure 5).
Among the 50 participants who reported fever and cough:

30% consulted a healthcare professional;
92% reported days missed from work or school, resulting in a combined total of 136 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-12

Number of Participants Reporting in Week 12: 2,056
Figure 5 - Text equivalent Influenza Outbreak Surveillance

In week 12, 38 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (19), acute care facilities (8) and other settings (11). Eleven new ILI outbreaks (LTCF (8) and schools and daycares (3)) were also reported in week 12. Among the outbreaks with available subtype information (12), 92% (11) were associated with influenza A(H3N2).
To date this season, 633 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

371 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 94 in acute care facilities, and 138 were in other settings.
Among the 563 outbreaks for which the influenza type was available, 98% (550) were associated with influenza A.
Among the 243 outbreaks for which the influenza A subtype was available, 55% (125) were associated with influenza A(H1N1)pdm09;

To date this season, 134 ILI outbreaks have been reported; 75 occurred in LTCF, 55 in schools, and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-12

Figure 6 - Text equivalent Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 2,592 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1.
Hospitalizations (Table 2):

98.7% (2,558) were associated with influenza A
Among the 1,555 cases for which the influenza subtype was available, 1,366 (88%) were associated with A(H1N1)pdm09.
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 464 ICU admissions and 127 deaths have been reported.
- 43% (199) of reported ICU admissions were in adults aged 45-64 years.
- All but four ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	354	12	76.89
5-19	210	10	15.85
20-44	317	4	11.28
45-64	688	3	31.75
65+	989	5	81.70
Total	2558	34
%	98.7%	1.3%
Table 2 - Note 1 Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 - Note1

Pediatric Influenza Hospitalizations and Deaths

In week 12, 41 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Of the 41 hospitalizations, 34 (83%) were due to influenza A.
To date this season, 1,089 pediatric hospitalizations have been reported (Figure 8):

67% of cases were in children under 5 years of age.
97% (1,054) of cases have been associated with influenza A.
Among the 324 cases for which the influenza subtype was available, 289 (89%) were associated with A(H1N1)pdm09.

To date this season, 194 ICU admissions, and 10 deaths have been reported.

60% (117) of ICU admissions were in children under 5 years of age.
All but two of the ICU admissions have been associated with influenza A.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-12

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Figure 7 - Text equivalent Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-12

Figure 8 - Text equivalent Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 773 hospitalizations, 90 ICU admissions and 40 deaths have been reported (Figure 9):

718 (93%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
Among the 167 cases for which the influenza subtype was available, 103 (62%) were associated with A(H1N1)pdm09.
88% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 83% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-12

Figure 9 - Text equivalent Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,700 influenza viruses (233 A(H3N2), 1,415 A(H1N1) and 52 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

124 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

18 viruses belonged to genetic group 3C.2a.
102 viruses belonged to subclade 3C.2a1.
Three viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

82 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
27 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
63 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 17 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,375 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
40 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

18 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
12 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
22 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.
...

https://www.canada.ca/en/public-heal...h-23-2019.html

**Pathfinder** · April 5, 2019, 05:19 PM

FluWatch report: March 24, 2019 to March 30, 2019 (week 13)

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Organization: Public Health Agency of Canada
Date published: 2019-04-05

Related Topics

Overall Summary

Influenza activity continues to be reported in almost all regions in Canada.
Though A(H1N1) peaked at end of December, over the past five weeks a second smaller wave, dominated by A(H3N2), is being observed in most regions of the country.
Detections of influenza A(H3N2) have been steadily increasing since mid-January and accounted for 76% of subtyped influenza A detections this week; however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season.
Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.
The 2018-19 Seasonal Influenza Immunization Coverage Survey showed that coverage was low among adults aged 18-64 years (34%) and highest among seniors aged 65 years and older (70%).

On this page

Influenza/Influenza-like Illness Activity (geographic spread)

During week 13, the following influenza activity levels were reported (Figure 1):

21 regions reported localized activity: in Alta.(2), Ont.(6), Que.(2), N.S.(3), N.B.(3), P.E.I.(1), Y.T.(1) and N.L.(3).
26 regions reported sporadic activity: in B.C.(5), Alta.(3), Sask.(3), Man.(3), Ont.(1), Que.(4), N.B.(4), N.L.(1) and N.W.T.(2)
Six regions: in Man.(2), N.S.(1) and Nvt.(3) reported no activity.

Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-13

Figure 1 - Text equivalent Laboratory-Confirmed Influenza Detections

In week 13, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

The percentage of tests positive for influenza remained steady at 22%.
A total 1,579 laboratory detections of influenza were reported, of which 91% were influenza A.
Influenza A(H3N2) accounted for 76% of subtyped influenza A detections.
Detections of influenza A(H3N2) have been steadily increasing, from 93 detections in week 4 (mid-January) to 358 this week.

To date this season, 41,372 laboratory-confirmed influenza detections have been reported:

98% have been influenza A.
Among the 13,859 influenza A viruses subtyped, 79% have been A(H1N1)pdm09.
Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 31,770 laboratory-confirmed influenza cases (Table 1):

83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
58% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-13

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Figure 2 - Text equivalent Figure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-13

Figure 3 - Text equivalent

0-4	6148	1644	127	4377	130	6278	20%
5-19	4537	1366	281	2890	202	4739	15%
20-44	6059	1910	332	3817	137	6196	20%
45-64	6079	1832	345	3902	76	6155	19%
65+	8224	1360	1479	5385	178	8402	26%
Total	31047	8112	2564	20371	723	31770	100%
Table 1 - Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 - Note1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 13, 1.6% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-13

Number of Sentinels Reporting in Week 13: 79
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018
Figure 4 - Text equivalent Participatory Syndromic Surveillance

In week 13, 2,041 participants reported to FluWatchers, of which 49 (2.4%) reported symptoms of cough and fever (Figure 5).
Among the 49 participants who reported fever and cough:

16% consulted a healthcare professional;
67% reported days missed from work or school, resulting in a combined total of 110 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-13

Number of Participants Reporting in Week 13: 2,041
Figure 5 - Text equivalent Influenza Outbreak Surveillance

In week 13, 31 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (13), acute care facilities (7) and other settings (11). Three new ILI outbreaks (LTCF (2) and schools and daycares (1)) were also reported in week 13. Among the outbreaks with available subtype information (8), all (8) were associated with influenza A(H3N2).
To date this season, 664 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

385 (58%) outbreaks were in LTCF, 30 were in schools and daycares, 102 in acute care facilities, and 147 were in other settings.
Among the 603 outbreaks for which the influenza type was available, 98% (590) were associated with influenza A.
Among the 262 outbreaks for which the influenza A subtype was available, 51% (128) were associated with influenza A(H3N2);

To date this season, 137 ILI outbreaks have been reported; 77 occurred in LTCF, 56 in schools, and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-13

Figure 6 - Text equivalent Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 2,701 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1.
Hospitalizations (Table 2):

98.4% (2,659) were associated with influenza A
Among the 1,629 cases for which the influenza subtype was available, 1,380 (85%) were associated with A(H1N1)pdm09.
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 474 ICU admissions and 139 deaths have been reported.
- 43% (202) of reported ICU admissions were in adults aged 45-64 years.
- All but four ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	361	15	79.00
5-19	218	13	16.65
20-44	327	4	11.63
45-64	704	4	32.53
65+	1049	6	86.71
Total	2659	42
%	98.4%	1.6%
Table 2 - Note 1 Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 - Note1

Pediatric Influenza Hospitalizations and Deaths

In week 13, 30 pediatric (≤16 years of age) hospitalizations with influenza have been reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Of the 30 hospitalizations, 27 (90%) were due to influenza A.
To date this season, 1,116 pediatric hospitalizations have been reported (Figure 8):

67% of cases were in children under 5 years of age.
96% (1,076) of cases have been associated with influenza A.
Among the 330 cases for which the influenza subtype was available, 289 (89%) were associated with A(H1N1)pdm09.

To date this season, 197 ICU admissions, and 10 deaths have been reported.

60% (119) of ICU admissions were in children under 5 years of age.
All but six of the ICU admissions have been associated with influenza A.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-13

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Figure 7 - Text equivalent Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-13

Figure 8 - Text equivalent Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 812 hospitalizations, 98 ICU admissions and 43 deaths have been reported (Figure 9):

757 (93%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (59%) compared to adults <65 years of age (41%).
Among the 169 cases for which the influenza subtype was available, 105 (62%) were associated with A(H1N1)pdm09.
88% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 83% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-13

Figure 9 - Text equivalent Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 1,745 influenza viruses (244 A(H3N2), 1,445 A(H1N1) and 56 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

130 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

18 viruses belonged to genetic group 3C.2a.
108 viruses belonged to subclade 3C.2a1.
Three viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

85 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
29 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
64 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 17 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,404 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
41 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

15 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
19 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
22 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.
...

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**Pathfinder** · April 26, 2019, 04:02 PM

FluWatch report: April 14 to April 20, 2019 (Week 16)

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Organization: Public Health Agency of Canada
Date published: 2019-04-26

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Overall Summary

Influenza continues to circulate in many regions across the country.
The second smaller wave of influenza activity, dominated by A(H3N2), decreased this week.
Detections of influenza A(H3N2) have been steadily increasing since mid-January and account for 89% of subtyped influenza A detections this week; however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season.
Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.

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Influenza/Influenza-like Illness Activity (geographic spread)

During week 16, the following influenza activity levels were reported (Figure 1):

14 regions reported localized activity: in Man.(1), Ont.(7), Que.(2), N.B.(1), N.S.(2), and Y.T.(1).
22 regions reported sporadic activity: in B.C.(5), Man.(3), Que.(4), N.S.(2), N.B.(6), P.E.I (1) and N.W.T.(1)
Two regions: in Man.(1) and N.W.T.(1) reported no activity.

Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-16

Figure 1 - Text equivalent Laboratory-Confirmed Influenza Detections

In week 16, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

The percentage of tests positive for influenza decreased to 17% in week 16.
A total of 1,024 laboratory detections of influenza were reported, of which 85% were influenza A.
Influenza A(H3N2) accounted for 89% of subtyped influenza A detections.

To date this season, 44,970 laboratory-confirmed influenza detections have been reported:

97% have been influenza A.
Among the 15,235 influenza A viruses subtyped, 73% have been A(H1N1)pdm09.
Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year.

To date this season, detailed information on age and type/subtype has been received for 36,036 laboratory-confirmed influenza cases (Table 1):

83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
58% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-16

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Data for week 14 excludes subtyping results from one jurisdiction due to batch reporting of subtype information. The results for week 14 should be interpreted with caution.
Figure 2 - Text equivalent Figure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-16

Figure 3 - Text equivalent

0-4	6566	1679	213	4674	195	6761	19%
5-19	4967	1387	416	3164	330	5297	15%
20-44	6661	1990	536	4135	230	6891	19%
45-64	6757	1950	549	4258	92	6849	19%
65+	10027	1452	2341	6234	211	10238	28%
Total	34978	8458	4055	22465	1058	36036	100%
Table 1 ? Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 ? Note1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 16, 0.8% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-16

Number of Sentinels Reporting in Week 16: 91
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018
Figure 4 - Text equivalent Participatory Syndromic Surveillance

In week 16, 1,904 participants reported to FluWatchers, of which 46 (2.4%) reported symptoms of cough and fever (Figure 5).
Among the 46 participants who reported fever and cough:

13% consulted a healthcare professional;
65% reported days missed from work or school, resulting in a combined total of 92 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-16

Number of Participants Reporting in Week 16: 1,904
Figure 5 - Text equivalent Influenza Outbreak Surveillance

In week 16, 21 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (12) and other settings (9). Three new ILI outbreaks were reported: LTCF (2) and schools (1). Among the outbreaks with available subtype information (7), all were associated with influenza A(H3N2).
To date this season, 753 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

441 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 113 in acute care facilities, and 169 were in other settings.
Among the 662 outbreaks for which the influenza type was available, 98% (648) were associated with influenza A.
Among the 281 outbreaks for which the influenza A subtype was available, 54% (151) were associated with influenza A(H3N2);

To date this season, 151 ILI outbreaks have been reported; 85 occurred in LTCF, 61 in schools, one in other settings and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-16

Figure 6 - Text equivalent Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 2,932 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1.
Hospitalizations (Table 2):

98.4% (2,886) were associated with influenza A
Among the 1,670 cases for which the influenza subtype was available, 1,404 (84%) were associated with A(H1N1)pdm09.
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 536 ICU admissions and 165 deaths have been reported.
- 41% (221) of reported ICU admissions were in adults aged 45-64 years.
- All but seven ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	383	17	84.04
5-19	231	15	17.73
20-44	345	4	12.27
45-64	748	3	34.51
65+	1179	7	97.48
Total	2886	46
%	98.4%	1.6%
Table 2 ? Note 1 Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 ? Note1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,217 pediatric hospitalizations have been reported (Figure 7 & 8):

66% of cases were in children under 5 years of age.
95% (1,152) of cases have been associated with influenza A.
Among the 358 cases for which the influenza subtype was available, 299 (84%) were associated with A(H1N1)pdm09.

To date this season, 229 ICU admissions, and 10 deaths have been reported.

59% (135) of ICU admissions were in children under 5 years of age.
All but nine of the ICU admissions have been associated with influenza A.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-16

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Figure 7 - Text equivalent Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-16

Figure 8 - Text equivalent Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 901 hospitalizations, 105 ICU admissions and 50 deaths have been reported (Figure 9):

840 (93%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (60%) compared to adults <65 years of age (40%).
Among the 194 cases for which the influenza subtype was available, 106 (55%) were associated with A(H1N1)pdm09.
89% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 95% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-16

Figure 9 - Text equivalent Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 2,006 influenza viruses (353 A(H3N2), 1,553 A(H1N1) and 100 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

164 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

20 viruses belonged to genetic group 3C.2a.
139 viruses belonged to subclade 3C.2a1.
Four viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

111 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
78 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
71 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 18 viruses belonged to genetic group 3C.2a and 29 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,510 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
43 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

16 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
61 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017.
23 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.
...

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**Pathfinder** · May 10, 2019, 05:50 PM

FluWatch report: April 28 to May 4, 2019 (Week 18)

Overall Summary
Overall Summary
Overall Summary
Overall Summary

Influenza activity continues to decline overall despite ongoing circulation of influenza A(H3N2) and influenza B in many regions across the country.
Influenza A(H3N2) was the predominant subtype this week (84% of subtyped influenza A detections); however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season (71% of subtyped influenza A detections).
Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.

On this page

Influenza/Influenza-like Illness Activity (geographic spread)

During week 18, the following influenza activity levels were reported (Figure 1):

14 regions reported localized activity: in Ont.(6), Que.(3), N.B.(1), N.S.(1), and N.L.(3).
26 regions reported sporadic activity: in B.C.(5), Sask.(3), Man.(5), Que.(4), N.S.(1), N.B.(6), P.E.I (1), and N.W.T.(1)
Five regions in four different provinces reported no activity.

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Organization: Public Health Agency of Canada
Date published: 2019-05-10

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Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-18

Figure 1 - Text equivalent Laboratory-Confirmed Influenza Detections

In week 18, the following results were reported from sentinel laboratories across (Figures 2 and 3):

The percentage of tests positive for influenza decreased from 14% to 11% in week 18.
A total of 609 laboratory detections of influenza were reported, of which 76% were influenza A.
Influenza A(H3N2) accounted for 84% of subtyped influenza A detections.

To date this season, 46,549 laboratory-confirmed influenza detections have been reported:

96% have been influenza A.
Among the 15,749 influenza A viruses subtyped, 71% have been A(H1N1)pdm09.
Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year. The percentage of tests positive for influenza B in week 18 was similar to the previous week.

To date this season, detailed information on age and type/subtype has been received for 37,331 laboratory-confirmed influenza cases (Table 1):

83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
58% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-18

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Data for week 14 excludes subtyping results from one jurisdiction due to batch reporting of subtype information. The results for week 14 should be interpreted with caution.
Figure 2 - Text equivalent Figure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-18

Figure 3 - Text equivalent

0-4	6673	1688	238	4747	261	6934	19%
5-19	5082	1388	458	3236	422	5504	15%
20-44	6796	2005	577	4214	291	7087	19%
45-64	6899	1954	614	4331	108	7007	19%
65+	10560	1474	2579	6507	239	10799	29%
Total	36010	8509	4466	23035	1321	37331	100%
Table 1 ? Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 ? Note1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 18, 0.7% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-18

Number of Sentinels Reporting in Week 18: 63
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018
Figure 4 - Text equivalent Participatory Syndromic Surveillance

In week 18, 1,951 participants reported to FluWatchers, of which 38 (1.9%) reported symptoms of cough and fever (Figure 5).
Among the 38 participants who reported fever and cough:

26% consulted a healthcare professional;
79% reported days missed from work or school, resulting in a combined total of 81 missed days of work or school.

Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-18

Number of Participants Reporting in Week 18: 1,951
Figure 5 - Text equivalent Influenza Outbreak Surveillance

In week 18, 11 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (7) acute care facilities (1) and other settings (3). No new ILI outbreaks were reported. Among the outbreaks with available information (9), 8 were associated with influenza A (of which 3 were associated with A(H3N2)), and one outbreak was associated with influenza B.
To date this season, 819 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

484 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 118 in acute care facilities, and 187 were in other settings.
Among the 733 outbreaks for which the influenza type was available, 98% (716) were associated with influenza A.
Among the 315 outbreaks for which the influenza A subtype was available, 58% (184) were associated with influenza A(H3N2);

To date this season, 151 ILI outbreaks have been reported; 85 occurred in LTCF, 61 in schools, one in other settings and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-18

Figure 6 - Text equivalent Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 3,075 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1.
Hospitalizations (Table 2):

97.7% (3,005) were associated with influenza A
Among the 1,696 cases for which the influenza subtype was available, 1,414 (83%) were associated with A(H1N1)pdm09.
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 555 ICU admissions and 179 deaths have been reported.
- 41% (227) of reported ICU admissions were in adults aged 45-64 years.
- All but eight ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	394	21	87.19
5-19	235	20	18.38
20-44	351	9	12.65
45-64	775	6	35.89
65+	1250	14	103.89
Total	3005	70
%	97.7%	2.3%
Table 2 ? Note 1 Influenza-associated hospitalizations are reported by Alberta, Manitoba, New Brunswick, Newfoundland and Labrador, Northwest Territories, Nova Scotia, Prince Edward Island and Yukon. Only hospitalizations that require intensive medical care are reported by Saskatchewan. The cumulative rate of hospitalizations is calculated using the total population by age-group in participating provinces and territories. Return to Table 2 ? Note1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,265 pediatric hospitalizations have been reported (Figure 7 & 8):

66% of cases were in children under 5 years of age.
94% (1,187) of cases have been associated with influenza A.
Among the 373 cases for which the influenza subtype was available, 305 (82%) were associated with A(H1N1)pdm09.

To date this season, 243 ICU admissions, and 10 deaths have been reported.

58% (142) of ICU admissions were in children under 5 years of age.
All but 12 of the ICU admissions have been associated with influenza A.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-18

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Figure 7 - Text equivalent Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-18

Figure 8 - Text equivalent Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 936 hospitalizations, 111 ICU admissions and 51 deaths have been reported (Figure 9):

869 (93%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (60%) compared to adults <65 years of age (40%).
Among the 202 cases for which the influenza subtype was available, 106 (52%) were associated with A(H1N1)pdm09.
89% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 86% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-18

Figure 9 - Text equivalent Influenza Strain Characterizations

Since September 1, 2018, the National Microbiology Laboratory (NML) has characterized 2,124 influenza viruses (418 A(H3N2), 1,575 A(H1N1) and 131 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

191 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

20 viruses belonged to genetic group 3C.2a.
166 viruses belonged to subclade 3C.2a1.
Four viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

141 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
86 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
97 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 19 viruses belonged to genetic group 3C.2a and 107 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,532 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
43 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

24 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
84 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017. Sequence analysis showed that 83 viruses that showed reduced titer had a three amino acid deletion (162-164) in the HA gene.
23 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.
...

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**Pathfinder** · May 17, 2019, 01:58 PM

FluWatch report: May 5 to May 11, 2019 (Week 19)

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Organization: Public Health Agency of Canada
Date published: 2019-05-17

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Overall Summary

Influenza activity continues to decline overall.
Influenza A(H3N2) was the predominant subtype this week (83% of subtyped influenza A detections); however, influenza A(H1N1)pdm09 remains the predominant subtype to date this season (71% of subtyped influenza A detections).
Detections of influenza A continue to be greater than those of influenza B. There is currently very little influenza B circulation compared to previous seasons.

On this page

Influenza/Influenza-like Illness Activity (geographic spread)

During week 19, the following influenza activity levels were reported (Figure 1):

7 regions reported localized activity: in Ont.(4), Que.(3).
29 regions reported sporadic activity: in B.C.(4), Sask.(2), Man.(5), Ont. (3), Que.(3), N.S.(2), N.B.(6), N.L.(1), Nvt. (2) and N.W.T.(1)
12 regions in 9 different provinces and territories reported no activity.

Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-19

Figure 1 - Text equivalentLaboratory-Confirmed Influenza Detections

In week 19, the following results were reported from sentinel laboratories across (Figures 2 and 3):

The percentage of tests positive for influenza increased slightly from 11% to 12% in week 19.
A total of 592 laboratory detections of influenza were reported, of which 76% were influenza A.
Influenza A(H3N2) accounted for 83% of subtyped influenza A detections.

To date this season, 47,143 laboratory-confirmed influenza detections have been reported:

96% have been influenza A.
Among the 15,938 influenza A viruses subtyped, 71% have been A(H1N1)pdm09.
Influenza B often circulates later in the season in Canada (Feb-Apr). Fewer influenza B detections have been reported this season compared to recent seasons at this time of year. The percentage of tests positive for influenza B in week 19 was similar to the previous week.

To date this season, detailed information on age and type/subtype has been received for 37,844 laboratory-confirmed influenza cases (Table 1):

83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
58% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-19

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Data for week 14 excludes subtyping results from one jurisdiction due to batch reporting of subtype information. The results for week 14 should be interpreted with caution.
Figure 2 - Text equivalentFigure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-19

Figure 3 - Text equivalent

0-4	6707	1689	248	4770	286	6993	18%
5-19	5127	1389	471	3267	482	5609	15%
20-44	6847	2012	596	4239	308	7155	19%
45-64	6964	1963	632	4369	115	7079	19%
65+	10761	1480	2667	6614	247	11008	29%
Total	36406	8533	4614	23259	1438	37844	100%
Table 1 ? Note 1UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 ? Note1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 19, 0.8% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-19

Number of Sentinels Reporting in Week 19: 72
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018
Figure 4 - Text equivalentParticipatory Syndromic Surveillance

FluWatchers surveillance has ended for the 2018-19 influenza season. On average 2,097 participants reported to FluWatchers each week, resulting in 64,672 questionnaires completed this season. The proportion of participants reporting fever and cough peaked in week 51 at 3.9% (Figure 5). Approximately 63% of FluWatchers participants reported being vaccinated for influenza in the 2018-19 season.
Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-18

Number of Participants Reporting in Week 18: 1,951

Figure 5 - Text equivalentInfluenza Outbreak Surveillance

In week 19, 11 new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (8) acute care facilities (1) and other settings (2). Four new ILI outbreaks were reported in LTCF. Among the outbreaks with available information (11), 10 were associated with influenza A (of which 2 were associated with A(H3N2)), and one outbreak was associated with influenza B.
To date this season, 838 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

496 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 120 in acute care facilities, and 192 were in other settings.
Among the 752 outbreaks for which the influenza type was available, 98% (734) were associated with influenza A.
Among the 323 outbreaks for which the influenza A subtype was available, 59% (192) were associated with influenza A(H3N2);

To date this season, 157 ILI outbreaks have been reported; 91 occurred in LTCF, 61 in schools, one in other settings and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-19

Figure 6 - Text equivalentSevere Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 3,092 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1. Note that data from one participating jurisdiction has not been available since surveillance week 13, so these figures are an underestimate of cases for this season.
Hospitalizations (Table 2):

97.6% (3,018) were associated with influenza A
Among the 1,704 cases for which the influenza subtype was available, 1,414 (83%) were associated with A(H1N1)pdm09.
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 555 ICU admissions and 182 deaths have been reported.
- 41% (227) of reported ICU admissions were in adults aged 45-64 years.
- All but eight ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	394	23	87.61
5-19	235	20	18.38
20-44	354	10	12.79
45-64	776	7	35.98
65+	1259	14	104.63
Total	3018	74
%	97.6%	2.4%
Table 2 ? Note 1Influenza-associated hospitalizations are reported by N.L., P.E.I, N.S., N.B., Man., Alb., Y.T. and N.W.T. Only hospitalizations that require intensive medical care are reported by Sask. The cumulative rate of hospitalizations is calculated using the population by age-group in participating provinces and territories. Return to Table 2 ? Note1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,280 pediatric hospitalizations have been reported (Figure 7 & 8):

66% of cases were in children under 5 years of age.
93% (1,192) of cases have been associated with influenza A.
Among the 375 cases for which the influenza subtype was available, 305 (81%) were associated with A(H1N1)pdm09.

To date this season, 246 ICU admissions, and 10 deaths have been reported.

58% (142) of ICU admissions were in children under 5 years of age.
All but 13 (95%) of the ICU admissions have been associated with influenza A; 84% of the 105 cases for which the influenza A subtype was available were associated with A(H1N1)pdm09.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-19

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Figure 7 - Text equivalentFigure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-19

Figure 8 - Text equivalentAdult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 942 hospitalizations, 115 ICU admissions and 54 deaths have been reported (Figure 9):

873 (93%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (60%) compared to adults <65 years of age (40%).
Among the 204 cases for which the influenza subtype was available, 107 (52%) were associated with A(H1N1)pdm09.
86% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 87% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-19

Figure 9 - Text equivalentInfluenza Strain Characterizations

From September 1, 2018 to 16 May, 2019, the National Microbiology Laboratory (NML) has characterized 2 170 influenza viruses (440 A(H3N2), 1,594 A(H1N1) and 136 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

191 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

20 viruses belonged to genetic group 3C.2a.
168 viruses belonged to subclade 3C.2a1.
Four viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

148 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
99 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
101 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 20 viruses belonged to genetic group 3C.2a and 116 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,551 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
43 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

25 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
88 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017. Sequence analysis showed that 87 viruses that showed reduced titer had a three amino acid deletion (162-164) in the HA gene.
23 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.
...

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**Pathfinder** · May 25, 2019, 05:49 PM

FluWatch report: May 12 to May 18, 2019 (Week 20)

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Organization: Public Health Agency of Canada
Date published: 2019-05-24

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Overall Summary

Influenza activity in Canada continues to decline. All indicators of influenza activity are decreasing and within the expected range for this time of year.
Influenza A(H3N2) and influenza B continue to co-circulate; however, the level of influenza B circulation continues to be very low compared to previous seasons.
This week, detections of influenza A continue to be greater than those of influenza B, and 85% of subtyped influenza A detections were A(H3N2).
Influenza A(H1N1)pdm09 remains the predominant subtype overall for the 2018-19 season (70% of subtyped influenza A detections).
This is the last weekly FluWatch report for the 2018-19 season. Monthly reports will be published over the summer on the last Friday of each month: June 28, July 26, and August 30. Weekly reporting of laboratory detections of respiratory viruses will continue via our Respiratory Virus Detections Surveillance System.

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Influenza/Influenza-like Illness Activity (geographic spread)

During week 20, the following influenza activity levels were reported (Figure 1):

6 regions reported localized activity: in Man.(1), and Ont.(5).
25 regions reported sporadic activity: in B.C.(5), Sask.(3), Man.(3), Ont. (2), Que.(6), N.S.(1), N.B.(4), and P.E.I.(1).
13 regions in 6 different provinces and territories reported no activity.

Figure 1 ? Map of overall influenza/ILI activity by province and territory, Canada, week 2019-20

Figure 1 - Text equivalent Laboratory-Confirmed Influenza Detections

In week 20, the following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

The percentage of tests positive for influenza decreased from 12% to 10% in week 20.
A total of 469 laboratory detections of influenza were reported, of which 72% were influenza A.
Influenza A(H3N2) accounted for 85% of subtyped influenza A detections.

To date this season, 47,622 laboratory-confirmed influenza detections have been reported:

96% have been influenza A.
Among the 16,126 influenza A viruses subtyped, 70% have been A(H1N1)pdm09.
Fewer influenza B detections have been reported this season compared to recent seasons at this time of year. The percentage of tests positive for influenza B in week 20 was similar to the previous week.

To date this season, detailed information on age and type/subtype has been received for 38,249 laboratory-confirmed influenza cases (Table 1):

83% of all influenza A(H1N1)pdm09 detections have been reported in individuals younger than 65 years of age.
58% of all influenza A(H3N2) detections have been reported in adults 65 years of age and older.

For more detailed weekly and cumulative influenza data, see the text descriptions for (Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.
Figure 2 ? Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2018-35 to 2019-20

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period of seasonal influenza activity.
Data for week 14 excludes subtyping results from one jurisdiction due to batch reporting of subtype information. The results for week 14 should be interpreted with caution.
Figure 2 - Text equivalent Figure 3 ? Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2018-35 to 2019-20

Figure 3 - Text equivalent

0-4	6739	1691	257	4791	306	7045	18%
5-19	5154	1392	484	3278	524	5678	15%
20-44	6885	2019	613	4253	337	7222	19%
45-64	7025	1973	668	4384	123	7148	19%
65+	10902	1485	2749	6668	254	11156	29%
Total	36705	8560	4771	23374	1544	38249	100%
Table 1 ? Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available. Return to Table 1 ? Note1 referrer.

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 20, 0.8% of visits to healthcare professionals were due to influenza-like illness (ILI) (Figure 4).
Figure 4 ? Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2018-35 to 2019-20

Number of Sentinels Reporting in Week 20: 74
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2013-2014 to 2017-2018
Figure 4 - Text equivalent Participatory Syndromic Surveillance

FluWatchers surveillance has ended for the 2018-19 influenza season. On average 2,097 participants reported to FluWatchers each week, resulting in 64,672 questionnaires completed this season. The proportion of participants reporting fever and cough peaked in week 51 at 3.9% (Figure 5). Approximately 63% of FluWatchers participants reported being vaccinated for influenza in the 2018-19 season.
Figure 5 - Percentage of participants reporting cough and fever, Canada, weeks 2018-40 to 2019-18

Number of Participants Reporting in Week 18: 1,951
Figure 5 - Text equivalent Influenza Outbreak Surveillance

In week 20, three new laboratory-confirmed influenza outbreaks were reported: long-term care facilities (LTCF) (1) acute care facilities (1) and other settings (1). One new ILI outbreak was reported in a LTCF. All the influenza outbreaks were associated with influenza A.
To date this season, 848 laboratory-confirmed influenza outbreaks have been reported (Figure 6):

504 (59%) outbreaks were in LTCF, 30 were in schools and daycares, 121 in acute care facilities, and 193 were in other settings.
Among the 761 outbreaks for which the influenza type was available, 98% (743) were associated with influenza A.
Among the 327 outbreaks for which the influenza A subtype was available, 60% (196) were associated with influenza A(H3N2);

To date this season, 160 ILI outbreaks have been reported; 94 occurred in LTCF, 61 in schools, one in other settings and four in acute care facilities.
Figure 6 ? Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2018-35 to 2019-20

Figure 6 - Text equivalent Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 3,097 influenza-associated hospitalizations have been reported by participating provinces and territoriesFootnote1. Note that data from one participating jurisdiction has not been available since surveillance week 13, so these figures are an underestimate of cases for this season.
Hospitalizations (Table 2):

97.6% (3,023) were associated with influenza A
Among the 1,710 cases for which the influenza subtype was available, 1,415 (83%) were associated with A(H1N1)pdm09.
The highest estimated rate of hospitalization is among adults over 65 years of age.

Intensive Care Unit (ICU) cases and deaths:

To date this season 557 ICU admissions and 184 deaths have been reported.
- 41% (227) of reported ICU admissions were in adults aged 45-64 years.
- All but nine ICU admissions were associated with influenza A.
- All but one of the deaths were associated with influenza A.

0-4	395	23	87.82
5-19	235	20	18.38
20-44	355	10	12.83
45-64	777	7	36.03
65+	1261	14	104.79
Total	3023	74
%	97.6%	2.4%
Table 2 ? Note 1 Influenza-associated hospitalizations are reported by N.L., P.E.I, N.S., N.B., Man., Alb., Y.T. and N.W.T. Only hospitalizations that require intensive medical care are reported by Sask. The cumulative rate of hospitalizations is calculated using the population by age-group in participating provinces and territories. Return to Table 2 ? Note1

Pediatric Influenza Hospitalizations and Deaths

To date this season, 1,298 pediatric hospitalizations have been reported (Figure 7 & 8):

66% of cases were in children under 5 years of age.
93% (1,201) of cases have been associated with influenza A.
Among the 376 cases for which the influenza subtype was available, 305 (81%) were associated with A(H1N1)pdm09.

To date this season, 246 ICU admissions, and 10 deaths have been reported.

59% (148) of ICU admissions were in children under 5 years of age.
All but 16 (94%) of the ICU admissions have been associated with influenza A; 83% of the 106 cases for which the influenza A subtype was available were associated with A(H1N1)pdm09.
80% (8) of deaths occurred in children 2 to 4 years of age.
All deaths have been associated with influenza A.

Figure 7 ? Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2018-35 to 2019-20

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-19
Figure 7 - Text equivalent Figure 8 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2018-35 to 2019-20

Figure 8 - Text equivalent Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2018-19 season.
To date this season, 944 hospitalizations, 117 ICU admissions and 54 deaths have been reported (Figure 9):

873 (92%) hospitalizations were associated with influenza A.
A greater proportion of hospitalizations have been reported among adults ≥65 years of age (60%) compared to adults <65 years of age (40%).
Among the 207 cases for which the influenza subtype was available, 107 (52%) were associated with A(H1N1)pdm09.
87% of hospitalized cases reported more than one type of comorbid condition.
The most commonly reported comorbidity was endocrine disorders, which were reported in 87% of hospitalized cases.

Figure 9 - Cumulative numbers of adult hospitalizations (>20 years of age) with influenza by age-group reported by CIRN, Canada, 2018-19, weeks 2018-44 to 2019-20

Figure 9 - Text equivalent Influenza Strain Characterizations

From September 1, 2018 to 23 May, 2019, the National Microbiology Laboratory (NML) has characterized 2,252 influenza viruses (488 A(H3N2), 1,612 A(H1N1) and 152 B) that were received from Canadian laboratories.
Genetic Characterization of Influenza A(H3N2):

191 influenza A(H3N2) viruses did not grow to sufficient hemagglutination titer for antigenic characterization by hemagglutination inhibition (HI) assay. Therefore, NML has performed genetic characterization to determine the genetic group identity of these viruses.
Sequence analysis of the HA gene of the viruses showed that:

20 viruses belonged to genetic group 3C.2a.
168 viruses belonged to subclade 3C.2a1.
Four viruses belonged to 3C.3a.
One isolate could not be sequenced.

A/Singapore/INFIMH-16-0019/2016-like virus belongs to genetic group 3C.2a1 and is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
Antigenic Characterization:

Influenza A (H3N2):

162 influenza A(H3N2) viruses were antigenically characterized as A/Singapore/INFIMH-16-0019/2016-like by HI testing using antiserum raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
133 viruses showed reduced titer with ferret antisera raised against egg-propagated A/Singapore/INFIMH-16-0019/2016.
A/Singapore/INFIMH-16-0019/2016-like virus is the influenza A(H3N2) component of the 2018-19 Northern Hemisphere influenza vaccine.
101 influenza A(H3N2) viruses characterized belonged to genetic group 3C.2a1. 20 viruses belonged to genetic group 3C.2a and 116 to 3C.3a. Sequencing is pending for the remaining isolates.

Influenza A(H1N1):

1,569 A(H1N1) viruses characterized were antigenically similar to A/Michigan/45/2015, which is the influenza A(H1N1) component of the 2018-19 Northern Hemisphere influenza vaccine.
43 viruses showed reduced titer with ferret antisera raised against cell culture-propagated A/Michigan/45/2015

Influenza B:
Influenza B viruses can be divided into two antigenically distinct lineages represented by B/Yamagata/16/88 and B/Victoria/2/87 viruses. The recommended influenza B components for the 2018-19 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage).

29 influenza B viruses were characterized as B/Colorado/06/2017, which belong to the Victoria lineage and are included as an influenza B component of the 2018-19 Northern Hemisphere influenza vaccine.
100 viruses showed reduced titer with ferret antisera raised against cell culture-propagated B/Colorado/06/2017. Sequence analysis showed that 99 viruses that showed reduced titer had a three amino acid deletion (162-164) in the HA gene.
23 influenza B viruses were characterized as B/Phuket/3073/2013-like, which belongs to the Yamagata lineage and is included as an influenza B component of the 2018-19 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

Antiviral Resistance ? Amantadine:

449 influenza A (89 A(H3N2) and 360 A(H1N1)) viruses were tested for resistance to amantadine and it was found that:

All 449 influenza A viruses were resistant to amantadine.

Antiviral Resistance ? Oseltamivir:

1,287 influenza viruses (167 A(H3N2), 1,039 A(H1N1) and 81 B) were tested for resistance to oseltamivir and it was found that:

All 167 A(H3N2) viruses were sensitive to oseltamivir.
Of the 1,039 A(H1N1) viruses tested, 1,035 were sensitive to oseltamivir and four viruses were resistant to oseltamivir with a H275Y mutation.
All 81 B viruses were sensitive to oseltamivir.

Antiviral Resistance ? Zanamivir:

1,286 influenza viruses (167 A(H3N2), 1,038 H1N1 and 81 B) were tested for resistance to zanamivir and it was found that:

All 1,286 influenza viruses were sensitive to zanamivir.

Vaccine Monitoring

Vaccine monitoring refers to activities related to the monitoring of influenza vaccine coverage and effectiveness.
Vaccine Coverage

The Seasonal Influenza Immunization Coverage Survey is an annual telephone survey conducted between January and February that collects information related to the influenza vaccine in Canada. This survey measures vaccine coverage, which is the percentage of people who received the annual seasonal influenza vaccine in a specific influenza season.
In the 2018-19 influenza season, coverage was:

34% among adults aged 18 to 64 years.
- 31% among adults aged 18-64 wihout chronic diseases.
- 43% among adults aged 18 to 64 years with chronic diseases.
70% among seniors (aged 65 years and older).

All adults (≥18)	1568	36.6	2150	46.8	3726	41.8
18-64	1252	28.6	1640	39.9	2898	34.3
without chronic diseases	948	25.8	1171	36.1	2124	30.8
with chronic diseases	304	36.3	465	48.5	770	42.8
≥65	316	69.0	510	70.9	828	69.9
Table 3 ? Note 1 Excluded from stratified analysis: eight people who did not disclose their gender and four people (18-64 years old) who did disclose whether they had any chronic diseases. Return to Table 3 ? Note1 referrer.

Vaccine Effectiveness

Vaccine effectiveness (VE) is a measure of how well the influenza vaccine is able to prevent influenza illness. Throughout the influenza season, surveillance networks estimate how well the influenza vaccine is working. Estimates can vary depending on several factors such as the study methods; the population, setting and outcomes that are being studied; the type and mix of vaccine products; the stage of the season and the kinds of influenza viruses that are circulating when the study is conducted.
The community-based Canadian Sentinel Practitioner Surveillance Network (SPSN) published an interim VE estimate in January 2019 for A(H1N1)pdm09. Subsequently, given an atypical late-season wave of influenza A(H3N2),SPSN has undertaken an additional interim analysis to assess effectiveness of the 2018/19 influenza vaccine against medically-attended outpatient A(H3N2) illness. Vaccine effectiveness (VE) monitoring methods and results are available at the SPSN website.
Based on data collected as of March 30th, 2019 from more than 2800 patients from B.C., Alta., Ont., and Que., the 2018/19 northern hemisphere vaccine effectiveness has varied depending on the strain.

A(H1N1)pdm09: In the first interim analysis, VE against A(H1N1)pdm09 was 72% (95% CI: 60 to 81) overall, with substantial protection observed in all age groups. In the most recent analysis as of March 30th, estimates against A(H1N1)pmd09 have remained stable at approximately 70%.
A(H3N2): In the most recent analysis, VE against A(H3N2) was 23% (95% CI: -9 to 46) overall. As the confidence interval crosses zero, this estimate does not provide evidence of vaccine protection against medically-attended outpatient A(H3N2) illness.

The SPSN continues to monitor and will further update VE estimates at end of season.

https://www.canada.ca/en/public-heal...y-18-2019.html

Announcement

Canada FluWatch Weekly Reports 2018-2019 Season Week 20

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