FluWatch report: FluWatch report: December 3, 2017 to December 9, 2017 (week 49)
- Overall, influenza activity continues to increase across Canada; however many indicators such as hospitalizations, outbreaks and geographic spread remained similar to the previous week.
- The majority of influenza detections continue to be A(H3N2), although a substantially greater number of influenza B detections has also been reported compared to previous seasons.
- Several indicators of influenza activity are above the expected levels for this time of year, and most similar to levels observed during the 2014-15 influenza season, when A(H3N2) was the predominant circulating subtype.
- The majority of lab confirmations, hospitalizations and deaths have been among adults aged 65+.
- Since early November, an above average number of weekly pediatric hospitalizations have been reported by the IMPACT network.
- 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 definitions for the 2017-2018 season
Influenza/Influenza-like Illness Activity (geographic spread)
In week 49, 15 regions (AB (4), MB (1), SK (2) ON (7) and QC (1)) reported localized activity, and 25 regions (BC (5), AB (1) SK (1), MB (3), QC (5), NB (4), NS (2), PE(1), YK(1) and NT(2)) reported sporadic activity. Consistent with the early influenza activity this season, a greater number of regions are reporting sporadic and localized activity compared to previous seasons.
Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2017-49
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.
Laboratory-Confirmed Influenza Detections
In week 49, both influenza A and B detections continued to increase, with 17.7% of tests positive for influenza. The number (863) and percentage (13.6%) of influenza A detections for week 49 are above average but within expected levels. The number (258) and percentage of tests (4.1%) positive for influenza B in week 49 are well above expected levels. Current levels of influenza B detections are not typically seen until mid-February. 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 2017-49
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.
To date this season, 4,135 laboratory-confirmed influenza detections have been reported, of which 81% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 95% 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 2017-49
To date this season, detailed information on age and type/subtype has been received for 3,809 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 42% have been reported in adults 65 years of age and older. Among cases of influenza A(H3N2), adults aged 65+ represented 52% of cases, compared to 38% and 43% of cases reported at week 49 in the 2016-17 and 2014-15 season respectively.
|Age groups (years)||Cumulative (August 27, 2017 to December 9, 2017)|
|Influenza A||B||Influenza A and B|
|A Total||A(H1) pdm09||A(H3)||A (UnS)Table 1 Footnote 1||Total||#||%|
Syndromic/Influenza-like Illness Surveillance
Healthcare Professionals Sentinel Syndromic Surveillance
In week 49, 1.8% of visits to healthcare professionals were due to influenza-like illness; a decrease compared to the previous week, and above the 5-year average.
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2017-49
Number of Sentinels Reporting in Week 49: 128
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2016-17
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 49, 1,360 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 18% of these consulted a healthcare professional. Among participants who reported cough and fever, 82% reported days missed from work or school, resulting in a combined total of 98 missed days of work or school.
|Number of Participants Reporting||Percentage participants reporting Cough and Fever||Percentage of participants with cough and fever who consulted a healthcare professional||Percentage of participants with cough and fever who reported missed days from work or school||Number of missed days from work or school|
Influenza Outbreak Surveillance
In week 49, 27 new laboratory-confirmed influenza outbreaks were reported: 11 in long-term care facilities, four in hospitals, and 12 in other settings. Among the 26 with influenza type/subtype reported, four were associated with influenza B and 22 were associated with influenza A, of which 18 (82%) were influenza A(H3N2), 3 influenza A(unsubtyped), and one A(H1N1).
To date this season, 95 influenza/ILI outbreaks have been reported, of which 34 (36%) occurred in LTC facilities. Among the 82 outbreaks for which the influenza type/subtype was reported, 66 were associated with influenza A (of which 50 were A(H3N2)), 15 were associated with influenza B, and one was associated with a mix of A(H3N2) and B. Compared to recent influenza A(H3N2) seasons at week 49, the number of outbreaks reported this season has been greater than the 2016-17 and 2012-13 seasons, and similar to the 2014-15 season.
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2017-49
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
In week 49, 69 influenza-associated hospitalizations were reported by participating provinces and territories.
To date this season, 704 influenza-associated hospitalizations have been reported, 89% of which were associated with influenza A, and 490 cases (70%) were in adults 65 years of age or older. The number of cases is considerably elevated relative to this period in the previous two seasons. To date, 47 ICU admissions and 19 deaths have been reported.
Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2017-49
- 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.
Pediatric Influenza Hospitalizations and Deaths
In week 49, 31 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Of the 31 hospitaliations, 25 (81%) were due to influenza A(H3N2). Since week 45, the number of hospitalizations reported each week has been above the seven-season weekly averages.
To date this season, 91 pediatric hospitalizations have been reported by the IMPACT network, 76 of which were associated with influenza A. Eighteen ICU admissions and fewer than five deaths have been reported. Compared to recent influenza A(H3N2) seasons at week 49, the number of hospitalizations reported this season have been greater than the 2016-17 and 2012-13 seasons, and similar to the 2014-15 season.
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 2017-49
Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2017-49
Influenza Strain Characterizations
During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 168 influenza viruses [131 A(H3N2), 10 A(H1N1)pdm09 and 27 B viruses] that were received from Canadian laboratories.
Among influenza viruses characterized by hemagglutination inhibition assay during the 2017-18 season, most viruses were antigenically similar to the cell-culture propagated reference strains recommended by WHO.
|Strain Characterization Results||Count||Description|
|Influenza A (H3N2)|
|A/Hong Kong/4801/2014-like||31||Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent vaccine.|
|Influenza A (H1N1)|
|A/Michigan/45/2015-like||10||Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.|
|Reduced titer to B/Brisbane/60/2008
Viruses showed reduced titer 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.
|23||Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2017-18 Northern Hemisphere quadrivalent influenza vaccine.|
Genetic Characterization of A(H3N2) viruses
During the 2017-18 season, 100 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 74 A(H3N2) viruses belonged to genetic group 3C.2a and 26 viruses belonged to subclade 3C.2a1.
Additionally, of the 31 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 27 belonged to genetic group 3C.2a and three viruses belonged to subclade 3C.2a1. Sequencing is pending for the remaining 1 isolate.
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 four viruses characterized as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that two of 4 viruses had a two amino acid deletion in the HA gene. Sequence is pending for the remaining two viruses.
During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 169 influenza viruses for resistance to oseltamivir and zanamivir, and all viruses were sensitive (Table 4).
|Virus type and subtype||Oseltamivir||Zanamivir|
|# tested||# resistant (%)||# tested||# resistant (%)|
|A (H3N2)||132||0 (0%)||132||0 (0%)|
|A (H1N1)||10||0 (0%)||10||0 (0%)|
|B||27||0 (0%)||27||0 (0%)|
|TOTAL||169||0 (0%)||169||0 (0%)|
Note: Since the 2009 pandemic, all circulating influenza A viruses have been resistant to amantadine, and it is therefore not currently recommended for use in the treatment of influenza. During the 2017-18 season, the subset of influenza A viruses that were tested for resistance to amantadine were resistant.
Provincial and International Influenza Reports
Provincial Influenza Reports
- Alberta - Influenza Surveillance Report
- British Columbia - Influenza Surveillance
- Manitoba - Seasonal Influenza Reports
- New Brunswick - Influenza Surveillance Reports
- Newfoundland and Labrador - Surveillance and Disease Reports
- Nova Scotia - Respiratory Watch Report
- Ontario - Respiratory Pathogen Bulletin
- Prince Edward Island - Influenza Summary
- Saskatchewan - Influenza Reports
- Québec - Flash Grippe
International Influenza Reports
- Australia - Influenza Surveillance Report
- European Centre for Disease Prevention and Control - Surveillance reports and disease data on seasonal influenza
- New Zealand - Influenza Weekly Update
- Public Health England - Weekly national flu reports
- Pan-American Health Organization - Influenza Situation Report
- United States Centres for Disease Control and Prevention - Weekly Influenza Surveillance Report
- World Health Organization - Influenza update
- World Health Organization - FluNet
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