Overall Summary
- Overall, influenza activity in Canada continued to decrease, but parts of Central and Eastern Canada are still reporting localized activity.
- Many indicators of influenza activity are either near or below average for this time of year.
- Detections of influenza A were greater than those of influenza B.
- To date this season, the majority of laboratory-confirmed cases, hospitalizations and deaths with influenza have been among adults 65 years of age and older.
- For more information on the flu, see our Flu(influenza) web page.
On this page
- Influenza/ILI Activity (geographic spread)
- Laboratory Confirmed Influenza Detections
- Syndromic/Influenza-like Illness Surveillance
- Influenza Outbreak Surveillance
- Severe Outcomes Influenza Surveillance
- Influenza Strain Characterizations
- Antiviral Resistance
- Provincial and International Influenza Reports
- FluWatch Surveillance System Description and Definitions, 2017-18
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Organization:
Public Health Agency of Canada
Date published: 2018-05-11
Related Topics
Influenza/Influenza-like Illness Activity (geographic spread)
In week 18, 13 regions (MB(1), ON(6), QC(2), NB(1), NL(2) and PE(1)) reported localized activity. Eight regions (MB(2), NB(2), NS(1), YK(1) and NU(2)) reported no influenza activity.
Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-18 Note: Influenza/ILI activity levels, as represented on this map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, sentinel ILI rates and reported outbreaks. Please refer to detailed definitions at the end of the report. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.
Figure 1 - Text description Laboratory-Confirmed Influenza Detections
In week 18, the percentage of tests positive for influenza was 8%, a decrease from the previous week. Laboratory detections of influenza are steadily decreasing. In week 18, 367 positive influenza tests were reported, down from 526 tests reported in week 17. Influenza A accounted for 66% of influenza detections in week 18.
Overall, laboratory detections of influenza are below average for this time of year. For data on other respiratory virus detections, see 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 2017-35 to 2018-18
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.
Figure 2 - Text description To date this season, 63,853 laboratory-confirmed influenza detections have been reported, of which 56% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 90% of subtyped influenza A detections. 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 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-18
Figure 3 - Text description To date this season, detailed information on age and type/subtype has been received for 51,313 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (50%), and among cases of influenza A(H3N2) (59%) and influenza B (48%). Adults aged 20-64 represent 32% of cases overall and 29% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (933), the majority of influenza A(H1N1)pdm09 cases are among adults less than 65 years of age, with adults aged 20-64 and children 0-19 years accounting for 53% and 31% of cases respectively.
0-4 | 3139 | 157 | 557 | 2425 | 1477 | 4616 | 9% |
5-19 | 2298 | 129 | 539 | 1630 | 2548 | 4846 | 9% |
20-44 | 4226 | 256 | 1191 | 2779 | 2760 | 6986 | 14% |
45-64 | 4654 | 236 | 1442 | 2976 | 4677 | 9331 | 18% |
65+ | 14975 | 155 | 5461 | 9359 | 10559 | 25534 | 50% |
Total | 29292 | 933 | 9190 | 19169 | 22021 | 51313 | 100% |
Table 1 Notes Table 1 Note 1 UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available Return to table 1 note1referrer |
Healthcare Practitioners Sentinel Syndromic Surveillance
In week 18, 1.5% of visits to healthcare professionals were due to influenza-like illness (ILI).
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-18
Number of participants in week 18: 166
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2016-17
Figure 4 - Text description Participatory Syndromic Surveillance
FluWatchers is a participatory ILI surveillance system that relies on weekly voluntary submissions of syndromic information from Canadians across Canada.
In week 18, 1,270 participants reported to FluWatchers, of which 1% reported symptoms of cough and fever, and 0% of these consulted a healthcare professional. Among participants who reported cough and fever, 75% reported days missed from work or school, resulting in a combined total of 36 missed days of work or school. FluWatchers surveillance has ended for the 2017-18 season.
1270 | 1% | 0% | 75% | 36 |
In week 18, 11 laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, four were reported in long-term care facilities (LTC), three in hospitals and four in other settings. Among the ten outbreaks with influenza type/subtype reported, seven (70%) were associated with influenza A, two (20%) were associated with influenza B and one outbreak was associated with a mix or influenza A and B (10%).
To date this season, 1,789 influenza/ILI outbreaks have been reported, of which 1,102 (62%) occurred in LTC facilities. Among the 1,530 outbreaks for which the influenza type/subtype was reported, 843 (55%) were associated with influenza A and 617 (40%) were associated with influenza B, and 70 (5%) were associated with a mix of A and B.
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-18
Figure 5 - Text description Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 5,059 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote1. Among the hospitalizations, 3,373 (67%) were associated with influenza A, and 3,308 cases (65%) were in adults 65 years of age or older.
Additionally, 508 ICU admissions and 290 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (44%), followed by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (86%).
Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note1, weeks 2017-35 to 2018-18
Figure 6 - Text description Figure 6 note 1 Influenza-associated hospitalizations are reported by NL, PE, NS, NB, MB, AB, YT and NT. Only hospitalizations that require intensive medical care are reported by SK.
Return to figure 6 note1referrer
Pediatric Influenza Hospitalizations and Deaths
In week 18, 10 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 80% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07. The number of weekly reported hospitalizations are below the seven-season average.
To date this season, 1,066 pediatric hospitalizations have been reported by the IMPACT network, 663 (62%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A hospitalizations (39%). Among the 403 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).
Additionally, 183 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (31%), followed by children aged 5-9 years (26%). Among the ICU cases with available information, 63% were due to influenza A and approximately 46% had no reported previous or concurrent medical conditions. All but one reported deaths were among children over the age of two.
Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, weeks 2017-35 to 2018-18
Figure 7 - Text description Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-18
The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2016-18
Figure 8 - Text description Influenza Strain Characterizations
During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 3,571 influenza viruses [1,478 A(H3N2), 287 A(H1N1)pdm09 and 1,806 B viruses] that were received from Canadian laboratories.
Antigenic Characterization
Among influenza viruses characterized by hemagglutination inhibition (HI) assay during the 2017-18 season, most viruses were antigenically similar to the cell-culture propagated reference strains recommended by WHO.
A/Hong Kong/4801/2014-like | 296 | Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent vaccine. |
Reduced titer to A/Hong Kong/4801/2014 | 88 | These A(H3N2) viruses reacted poorly with antisera raised against cell-propagated A/Hong Kong/4801/2014, suggesting some antigenic differences. |
A/Michigan/45/2015-like | 287 | Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1)pdm09 component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine. |
B/Brisbane/60/2008-like (Victoria lineage) |
24 | Viruses antigenically similar to B/Brisbane/60/2008. B/Brisbane/60/2008 is the influenza B component of the 2017-18 Northern Hemisphere?s trivalent and quadrivalent influenza vaccine. |
Reduced titer to B/Brisbane/60/2008 (Victoria lineage) |
54 | These B/Victoria lineage viruses reacted poorly with antisera raised against cell-propagated B/Brisbane/60/2008, suggesting some antigenic differences. |
B/Phuket/3073/2013-like (Yamagata lineage) |
1728 | Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2017-18 Northern Hemisphere quadrivalent influenza vaccine. |
During the 2017-18 season, 1,094 A(H3N2) viruses did not grow to sufficient titers for antigenic characterization by HI assay. Therefore, genetic characterization was performed to determine to which genetic group they belong. Sequence analysis showed that 981 A(H3N2) viruses belonged to genetic group 3C.2a, 111 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.
Additionally, of the 384 influenza A(H3N2) viruses that were antigenically characterized , 267 belonged to genetic group 3C.2a and 26 viruses belonged to subclade 3C.2a1. The 88 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the remaining three virus isolates.
A/Hong Kong/4801/2014-like virus belongs to genetic group 3C.2a and is the influenza A/H3N2 component of the 2017-18 Northern Hemisphere influenza vaccine.
Genetic Characterization of Influenza B viruses
Of the 78 influenza B viruses characterized as B/ B/Brisbane/60/2008-like, 24 viruses were antigenically similar to the vaccine strain B/Brisbane/60/2008. Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that 49 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the remaining five virus isolates.
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