<TABLE border=0 cellSpacing=0 cellPadding=0><TBODY><TR><TD>May 15 to 21, 2011 (Week 20)
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Posted 2011-05-27
Overall Influenza Summary
- The 2010-11 influenza season in Canada is drawing to a close, with most regions of the country reporting sporadic or no activity. The ILI consultation rate, number of outbreaks, paediatric and adult hospitalizations all continue to decrease.
- Laboratory detections of both influenza A and B continue to decrease, and in week 20 the proportion of positive tests for parainfluenza viruses declined.
Note: This is the final weekly report for the 2010-11 influenza season. Bi-weekly reports will commence on June 10th (for weeks 21 and 22). However, laboratory detections reported through the RVDSS and influenza activity level maps will be updated weekly on the FluWatch website.
Influenza Activity and Outbreaks
In week 20, 4 regions reported localized activity: AB(1), NS(2) and NL(1); 21 regions reported sporadic activity; and 31 regions presented no activity (see Activity level Map). Three new outbreaks were reported in wk 20, one outbreak of influenza in a long-term care facility (LTCF) in Alberta, and 2 ILI outbreaks in communities in Nova Scotia.
Map of overall Influenza activity level by province and territory, Canada, Week 20
No Data
No Activity
Sporadic Activity
Localized Activity
Widespread Activity
Note: Influenza 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 (see graphs and tables) and reported outbreaks. Please refer to detailed definitions on the last page. For areas where no data is reported, late reports from these provinces and territories will appear on the FluWatch website.
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Number of influenza surveillance regions<SUP title="sub-regions within the province or territory as defined by the provincial/territorial epidemiologist. Graph may change as late returns come in">?</SUP> reporting widespread or localized influenza activity, Canada, by report week, 2010-2011 (N=56)
? sub-regions within the province or territory as defined by the provincial/territorial epidemiologist. Graph may change as late returns come in.
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Overall Number of Influenza Outbreaks, Canada, by Report Week, 2010-2011
Note that this was the first year that all the provinces and territories were reporting on influenza outbreaks in schools (greater than 10% absenteeism on any day most likely due to ILI) which has increased considerably the total number of outbreaks reported compared to previous years.
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ILI consultation rate
During week 20, the national ILI consultation rate was 10.0 consultations per 1,000 patient visits, which is decreased compared to the previous week and within the expected rate for this time of year (see ILI graph). Children 5-19 years of age had the highest consultation rates (21.6 per 1,000 consultations) in week 20.
Influenza-like illness (ILI) consultation rates, Canada, by report week, 2010-2011 compared to 1996/97 through to 2008/09 seasons
Note: No data available for mean rate in previous years for weeks 19 to 39 (1996-1997 through 2002-2003 seasons). Delays in the reporting of data may cause data to change retrospectively.
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Laboratory Surveillance Summary
The overall proportion of tests that were positive for influenza during week 20 was 2.9% (1.0% influenza A, 1.9% influenza B), which is decreased compared to week 19 (3.8%). The proportion of positive tests peaked in week 52 (see Influenza tests graph). Since the beginning of the season, 85.5% (16,847/19,706) of influenza virus detections have been influenza A viruses, of which 84.8% (5,578/6,578) of subtyped specimens have been A/H3N2. Detections of influenza B have been increasing steadily since week 03 and peaked in week 15. Through detailed case-based laboratory reporting where age data is provided, since August 29, 2010, 50.7% (2,059/4,059) of cases with A/H3N2 were aged 65 years or older. In contrast, the majority of cases with pandemic H1N1 2009 (94.5%, 751/795) and influenza B (90.3%, 1,348/1,492) were under 65 years of age (see Tests detailed table). Following an increasing proportion of positive tests for parainfluenza viruses since week 11, the proportion decreased in week 20 (see Respiratory viruses graph).
Weekly & Cumulative numbers of positive influenza specimens by Provincial Laboratories, Canada, 2010-2011
<TABLE class=widthFull border=1 cellSpacing=0 cellPadding=2><TFOOT><TR><TD class=fontSize85 colSpan=13>* Unsubtyped: The specimen was typed as influenza A, but no test for subtyping was performed. Specimens from NT, YT, and NU are sent to reference laboratories in other provinces. Note: Cumulative data includes updates to previous weeks; due to reporting delays, the sum of weekly report totals do not add up to cumulative totals.
</TD></TR></TFOOT><TBODY><TR class=alignCenter><TH class=bg-colour-blue rowSpan=3 scope=col>Reporting provinces</TH><TH class="bg-colour-blue fontSize85" colSpan=6 scope=colgroup>Weekly (May 15 to May 21, 2011)</TH><TH class="bg-colour-blue fontSize85" colSpan=6 scope=colgroup>Cumulative (August 29, 2010 to May 21, 2011)</TH></TR><TR class=alignCenter><TH class="bg-colour-blue fontSize85" colSpan=5 scope=colgroup>Influenza A</TH><TH class="bg-colour-blue fontSize85" scope=col>B</TH><TH class="bg-colour-blue fontSize85" colSpan=5 scope=colgroup>Influenza A</TH><TH class=bg-colour-blue scope=col>B</TH></TR><TR class=alignCenter><TH class="fontSize85 bg-colour-blue" scope=col>A Total</TH><TH class="fontSize85 bg-colour-blue" scope=col>A(H1)</TH><TH class="fontSize85 bg-colour-blue" scope=col>A(H3)</TH><TH class="fontSize85 bg-colour-blue" scope=col>Pand H1N1</TH><TH class="fontSize85 bg-colour-blue noWrap" scope=col>A (Un S)*</TH><TH class="fontSize85 bg-colour-blue" scope=col>Total</TH><TH class="fontSize85 bg-colour-blue" scope=col>A Total</TH><TH class="fontSize85 bg-colour-blue" scope=col>A(H1)</TH><TH class="fontSize85 bg-colour-blue" scope=col>A(H3)</TH><TH class="fontSize85 bg-colour-blue" scope=col>Pand H1N1</TH><TH class="fontSize85 bg-colour-blue noWrap" scope=col>A (Un S)*</TH><TH class="fontSize85 bg-colour-blue" scope=col>Total</TH></TR><TR><TH class=bg-colour-blue scope=row>BC</TH><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>477</TD><TD class=alignCenter>0</TD><TD class=alignCenter>200</TD><TD class=alignCenter>164</TD><TD class=alignCenter>113</TD><TD class=alignCenter>179</TD></TR><TR><TH class=bg-colour-blue scope=row>AB</TH><TD class=alignCenter>8</TD><TD class=alignCenter>0</TD><TD class=alignCenter>7</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>2</TD><TD class=alignCenter>1081</TD><TD class=alignCenter>0</TD><TD class=alignCenter>765</TD><TD class=alignCenter>279</TD><TD class=alignCenter>37</TD><TD class=alignCenter>736</TD></TR><TR><TH class=bg-colour-blue scope=row>SK</TH><TD class=alignCenter>2</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>1</TD><TD class=alignCenter>320</TD><TD class=alignCenter>0</TD><TD class=alignCenter>213</TD><TD class=alignCenter>30</TD><TD class=alignCenter>77</TD><TD class=alignCenter>175</TD></TR><TR><TH class=bg-colour-blue scope=row>MB</TH><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>515</TD><TD class=alignCenter>0</TD><TD class=alignCenter>56</TD><TD class=alignCenter>2</TD><TD class=alignCenter>457</TD><TD class=alignCenter>15</TD></TR><TR><TH class=bg-colour-blue scope=row>ON</TH><TD class=alignCenter>1</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>0</TD><TD class=alignCenter>8</TD><TD class=alignCenter>6884</TD><TD class=alignCenter>0</TD><TD class=alignCenter>2437</TD><TD class=alignCenter>275</TD><TD class=alignCenter>4172</TD><TD class=alignCenter>841</TD></TR><TR><TH class=bg-colour-blue scope=row>QC</TH><TD class=alignCenter>2</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>2</TD><TD class=alignCenter>17</TD><TD class=alignCenter>6026</TD><TD class=alignCenter>0</TD><TD class=alignCenter>957</TD><TD class=alignCenter>41</TD><TD class=alignCenter>5028</TD><TD class=alignCenter>757</TD></TR><TR><TH class=bg-colour-blue scope=row>NB</TH><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>959</TD><TD class=alignCenter>0</TD><TD class=alignCenter>669</TD><TD class=alignCenter>176</TD><TD class=alignCenter>114</TD><TD class=alignCenter>102</TD></TR><TR><TH class=bg-colour-blue scope=row>NS</TH><TD class=alignCenter>1</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>2</TD><TD class=alignCenter>272</TD><TD class=alignCenter>0</TD><TD class=alignCenter>80</TD><TD class=alignCenter>11</TD><TD class=alignCenter>181</TD><TD class=alignCenter>7</TD></TR><TR><TH class=bg-colour-blue scope=row>PE</TH><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>97</TD><TD class=alignCenter>0</TD><TD class=alignCenter>79</TD><TD class=alignCenter>16</TD><TD class=alignCenter>2</TD><TD class=alignCenter>7</TD></TR><TR><TH class=bg-colour-blue scope=row>NL</TH><TD class=alignCenter>3</TD><TD class=alignCenter>0</TD><TD class=alignCenter>2</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>2</TD><TD class=alignCenter>216</TD><TD class=alignCenter>0</TD><TD class=alignCenter>122</TD><TD class=alignCenter>6</TD><TD class=alignCenter>88</TD><TD class=alignCenter>40</TD></TR><TR><TH class=bg-colour-blue scope=row>Canada</TH><TD class=alignCenter>17</TD><TD class=alignCenter>0</TD><TD class=alignCenter>10</TD><TD class=alignCenter>1</TD><TD class=alignCenter>6</TD><TD class=alignCenter>34</TD><TD class=alignCenter>16847</TD><TD class=alignCenter>0</TD><TD class=alignCenter>5578</TD><TD class=alignCenter>1000</TD><TD class=alignCenter>10269</TD><TD class=alignCenter>2859</TD></TR></TBODY></TABLE>
Weekly & Cumulative numbers of positive influenza specimens by age groups reported through case-based laboratory reporting, Canada, 2010-2011*
<TABLE class=widthFull border=1 cellSpacing=0 cellPadding=2><TFOOT><TR><TD class=fontSize85 colSpan=11>* Please note that this table reflects the number of specimens for which demographic information was reported. These represent a subset of all positive influenza cases reported. Five provinces have reported detailed case-by-case data since the beginning of the season (BC, AB, SK, MB and ON). Delays in the reporting of data may cause data to change retrospectively.
</TD></TR></TFOOT><TBODY><TR class=bg-colour-yellow><TH rowSpan=3 scope=col>Age groups</TH><TH colSpan=5 scope=colgroup>Weekly
(May 15 to May 21, 2011)</TH><TH colSpan=5 scope=colgroup>Cumulative
(Aug. 29, 2010 to May 21, 2011)
</TH></TR><TR class=bg-colour-yellow><TH colSpan=4 scope=colgroup>Influenza A</TH><TH>B</TH><TH colSpan=4 scope=colgroup>Influenza A</TH><TH>B</TH></TR><TR class=bg-colour-yellow><TH scope=col>A Total</TH><TH scope=col>Pandemic H1N1</TH><TH scope=col>A/H3N2</TH><TH scope=col>A unsubtyped</TH><TH scope=col>Total</TH><TH scope=col>A Total</TH><TH scope=col>Pandemic H1N1</TH><TH scope=col>A/H3N2</TH><TH scope=col>A unsubtyped</TH><TH scope=col>Total</TH></TR><TR><TD><5</TD><TD class=alignCenter>4</TD><TD class=alignCenter>0</TD><TD class=alignCenter>2</TD><TD class=alignCenter>2</TD><TD class=alignCenter>1</TD><TD class=alignCenter>1015</TD><TD class=alignCenter>129</TD><TD class=alignCenter>738</TD><TD class=alignCenter>148</TD><TD class=alignCenter>410</TD></TR><TR><TD>5-19</TD><TD class=alignCenter>2</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>1</TD><TD class=alignCenter>1</TD><TD class=alignCenter>517</TD><TD class=alignCenter>103</TD><TD class=alignCenter>296</TD><TD class=alignCenter>118</TD><TD class=alignCenter>533</TD></TR><TR><TD>20-44</TD><TD class=alignCenter>1</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1</TD><TD class=alignCenter>0</TD><TD class=alignCenter>1082</TD><TD class=alignCenter>332</TD><TD class=alignCenter>530</TD><TD class=alignCenter>220</TD><TD class=alignCenter>291</TD></TR><TR><TD>45-64</TD><TD class=alignCenter>2</TD><TD class=alignCenter>0</TD><TD class=alignCenter>2</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>791</TD><TD class=alignCenter>187</TD><TD class=alignCenter>436</TD><TD class=alignCenter>168</TD><TD class=alignCenter>114</TD></TR><TR><TD>65+</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>2509</TD><TD class=alignCenter>44</TD><TD class=alignCenter>2059</TD><TD class=alignCenter>406</TD><TD class=alignCenter>144</TD></TR><TR><TD>Unknown</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>0</TD><TD class=alignCenter>231</TD><TD class=alignCenter>3</TD><TD class=alignCenter>224</TD><TD class=alignCenter>4</TD><TD class=alignCenter>1</TD></TR><TR><TD>Total</TD><TD class=alignCenter>9</TD><TD class=alignCenter>0</TD><TD class=alignCenter>5</TD><TD class=alignCenter>4</TD><TD class=alignCenter>2</TD><TD class=alignCenter>6145</TD><TD class=alignCenter>798</TD><TD class=alignCenter>4283</TD><TD class=alignCenter>1064</TD><TD class=alignCenter>1493</TD></TR></TBODY></TABLE>
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Influenza tests reported and percentage of tests positive, Canada, by report week, 2010-2011
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Percent positive influenza tests, compared to other respiratory viruses, Canada, by reporting week, 2010-2011
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Antigenic Characterization
Between September 1 and May 27, 2011, the National Microbiology Laboratory (NML) has antigenically characterized 950 influenza viruses that were received from provincial laboratories: 270 A/H3N2, 142 pandemic H1N1 2009 and 538 B viruses. Of the 270 influenza A/H3N2 viruses characterized, 267 (98.9%) were antigenically related to A/Perth/16/2009, which is the influenza A/H3N2 component recommended for the 2010-11 influenza vaccine. Three viruses (1.1%) tested showed reduced titer with antiserum produced against A/Perth/16/2009. Of the 142 pandemic H1N1 2009 viruses characterized, 140 (98.6%) were antigenically related to the pandemic vaccine virus A/California/7/2009, which is the recommended H1N1 component for the 2010-11 influenza vaccine. Two viruses (1.4%) tested showed reduced titer with antiserum produced against A/California/7/2009. Of the 538 influenza B viruses characterized, 509 (94.6%) were antigenically related to B/Brisbane/60/08 (Victoria lineage), which is the recommended influenza B component for the 2010-11 influenza vaccine. Four of the 509 viruses tested showed reduced titer with antisera produced against B/Brisbane/60/08. Twenty-five (4.6%) influenza B viruses were characterized as B/Wisconsin/01/2010-like, which belongs to the Yamagata lineage. B/Wisconsin/01/2010-like viruses are antigenically and genetically different from the previous Yamagata lineage vaccine strain B/Florida/04/2006.
Antiviral Resistance
Since the beginning of the 2010-2011 season, NML has tested 633 influenza A isolates (474 A/H3N2 and 159 pandemic H1N1 2009) for amantadine resistance and found that 473 influenza A/H3N2 were resistant and one was sensitive. All 159 influenza A/H1N1 viruses were resistant to amantadine. Of 923 influenza viruses (248 A/H3N2, 146 pandemic H1N1 2009, and 529 influenza B) tested for resistance to oseltamivir, 247 A/H3N2 viruses were sensitive and one was resistant with the E119V mutation. The resistant case was associated with oseltamivir prophylaxis/treatment. Of the 146 pandemic H1N1 2009 isolates tested for oseltamivir resistance, 145 were sensitive and one was resistant with the H275Y mutation. The resistant case was associated with oseltamivir treatment. Of the 529 B virus isolates tested, 528 were sensitive to oseltamivir and one was resistant with the D198N mutation. Of 914 influenza viruses (244 A/H3N2, 143 pandemic H1N1 2009, and 527 influenza B) tested for zanamivir resistance all 244 A/H3N2 and 143 pandemic H1N1 2009 isolates were found to be sensitive. Of the 527 B virus isolates tested, 526 were sensitive to zanamivir and one was resistant with the D198N mutation.
Severe Illness Surveillance
Note that all numbers are preliminary and numbers may fluctuate because of delays in reporting
Paediatric Influenza Hospitalizations and Deaths
In week 20, 6 new laboratory-confirmed influenza-associated paediatric (16 years of age and under) hospitalizations were reported through the Immunization Monitoring Program Active (IMPACT) network: all with influenza B, from BC(1), QC(4) and NL(1). Influenza A was associated with the majority of hospitalizations earlier in the season (weeks 47 to 09). Since week 10, however, influenza B accounted for more cases than influenza A each week. Six paediatric deaths have been reported via IMPACT this season: 3 children between 6 and 23 months old, two with pandemic H1N1 2009 and one with influenza B; two children between 2 and 4 years old, both with influenza B; and one child between 10 and 16 years old with influenza A/H3. All cases had underlying comorbidities.
Since the beginning of the season, 668 hospitalizations with laboratory-confirmed influenza have been reported: 103 (15.4%) as influenza A/H3N2, 23 (3.4%) pandemic H1N1 2009, 326 (48.8%) as un-subtyped influenza A, and 216 (32.3%) influenza B. The distribution of cases to date by age group was as follows: 16.8% among 0-5 month olds; 27.5% among 6-23 month olds; 28.7% among the 2-4 year-olds; 16.5% among 5-9 year-olds; and 10.5% among children 10-16 years old.
Adult Influenza Hospitalizations and Deaths
During week 20, no new hospitalizations with laboratory-confirmed influenza among adults (16 years of age and older) were reported through the Canadian Nosocomial Infection Surveillance Program (CNISP). Since the beginning of the season, 969 hospitalized cases have been reported: 202 (20.8%) A/H3N2, 48 (5.0%) pandemic H1N1 2009, 644 (66.5%) influenza A unsubtyped, and 75 (7.7%) influenza B, from all reporting provinces. To date, 651 of the 969 (67.2%) cases were aged 65 years or older and 437 (45.1%) were males.
Aggregate Influenza Hospitalizations and Deaths
Nine provinces and territories (excluding BC, QC, NB and NU) currently conduct severe outcomes surveillance and report weekly numbers of hospitalizations, ICU admissions and deaths with laboratory-confirmed influenza. In week 20, no deaths with influenza were reported. Among the 224 fatal cases reported since the beginning of the influenza season, influenza A/H3N2 was identified in 60.7% (136/224), unsubtyped influenza A in 28.1% (63/224), pandemic H1N1 2009 in 6.7% (15/224), and influenza B in 4.5% (10/224). Seventy-nine percent (177/224) of these fatal cases were among persons 65 years of age or older, and another 11% (25/224) were between the ages of 45 and 64 years old, in keeping with the age-groups usually affected by A/H3N2.
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