FluWatch report: December 31, 2017 to January 6, 2018 (week 1)
- Overall, influenza activity in Canada is high and continues to increase. Most indicators of influenza activity increased in week 01, and are in the higher range of expected levels for this time of year.
- The majority of influenza detections continue to be A(H3N2), although the proportion of detections that are influenza B has been increasing steadily
- Influenza B is circulating much earlier than usual this season. The number of influenza B detections remains substantially greater this season compared to previous years.
- To date this season, the majority of lab confirmations, hospitalizations and deaths 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 definitions for the 2017-2018 season
Influenza/Influenza-like Illness Activity (geographic spread)
In week 01, an increasing number of regions reported localized or widespread influenza activity; nine regions (BC(2), ON(3), QC(3) and PE(1)) reported widespread activity, and 27 regions (BC(2), AB(4), SK(1), MB (4), ON(4), QC(3), NB(5), NS(3) and NT(1)) reported localized activity.
Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-01
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 01, both influenza A and B detections continued to increase although the rate of increase in influenza A detections was smaller compared to influenza B. The slowing of influenza A detections may indicate that we are approaching the peak of the season for influenza A, at the national level. However, the number of influenza B detections increased 52% compared to the previous week to1,529 in week 01, which is the highest weekly value observed over the past seven seasons.
The proportion of tests positive for influenza increased slightly from 28% in week 52 to 30% in week 01. The proportion of influenza detections that are influenza B has been increasing steadily since week 42. In week 01, 64% of detections were influenza A and 36% influenza B.
The number (2,732) and percentage (19.3%) of influenza A detections for week 01 are within the range of expected levels for this time of year. The number (1,529) and percentage of tests (10.8%) positive for influenza B in week 01 continue to be well above expected levels. Influenza B is circulating much earlier than usual this season. Twenty times the number of influenza B detections have been reported this season compared to the same period during the past seven seasons. 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 2018-01
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, 15,572 laboratory-confirmed influenza detections have been reported, of which 71% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 94% 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 2018-01
To date this season, detailed information on age and type/subtype has been received for 14,038 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 47% have been reported in adults 65 years of age and older. Among cases of influenza A(H3N2), adults 65 years of age and older represented 52% of cases, compared to 41% and 56% of cases reported in the same period in the 2016-17 and 2014-15 season, respectively. Cases of influenza B this season were distributed more evenly across all age-groups, but the largest proportion of cases was still among adults 65 years of age and older (41%), followed by adults 45-64 years of age (23%).
|Age groups (years)||Cumulative (August 27, 2017 to January 6, 2018)|
|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 01, 4.7% of visits to healthcare professionals were due to influenza-like illness (ILI); an increase 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 2018-01
Number of Sentinels Reporting in Week 1: 116
The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2017-18
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 01, 1,406 participants reported to FluWatchers, of which 5% reported symptoms of cough and fever, and 22% of these consulted a healthcare professional. Among participants who reported cough and fever, 84% reported days missed from work or school, resulting in a combined total of 186 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 01, the number of reported laboratory-confirmed outbreaks of influenza increased compared to the previous week. In week 01, 148 new influenza outbreaks were reported: 98 in long-term care facilities, 12 in hospitals, and 38 in other settings. Among the 120 outbreaks with influenza type/subtype reported, 44 (37%) were associated with influenza B, and 73 were associated with influenza A, of which 20 were influenza A(H3N2) and 53 influenza A(unsubtyped). Three outbreaks were associated with a mix of influenza A and B.
To date this season, 486 influenza/ILI outbreaks have been reported, of which 282 (58%) occurred in LTC facilities. Among the 403 outbreaks for which the influenza type/subtype was reported, 286 were associated with influenza A (of which 153 were A(H3N2), 132 were A(unsubtyped) and one was A(H1N1)pdm09), 101 were associated with influenza B, and 16 were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 01, the number of cumulative outbreaks reported this season has been greater than during the 2016-17 and 2012-13 seasons, and lower compared to the 2014-15 season.
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-01
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
In week 01, 128 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. In keeping with the early influenza activity this season, the number of hospitalizations is considerably elevated relative to the same period in the previous two seasons.
To date this season, 1,850 influenza-associated hospitalizations have been reported, 83% of which were associated with influenza A, and 1,254 cases (68%) were in adults 65 years of age or older. To date, 162 ICU admissions and 54 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 2018-01
- 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 01, the number of laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations reported by the Immunization Monitoring Program Active (IMPACT) network decreased compared to the previous week. In week 01, 46 hospitaliations were reported, of which 25 (54%) were due to influenza A. The proportion of cases associated with influenza B has been increasing over the past three weeks. The number of weekly hospitalizations has been above the seven-season average since week 45.
To date this season, 253 pediatric hospitalizations have been reported by the IMPACT network, 177 (70%) of which were associated with influenza A. Forty-one ICU admissions and fewer than five deaths have been reported. Compared to recent influenza A(H3N2) seasons at week 01, the cumulative number of hospitalizations reported this season has been greater than the 2016-17 season, but below the 2014-15 and 2012-13 seasons.
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 2018-01
Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-01
- Figure 8 Footnote 1
The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18
Influenza Strain Characterizations
During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 351 influenza viruses [229 A(H3N2), 26 A(H1N1)pdm09 and 96 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||54||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||26||Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.|
|1||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
|5||These B/Victoria lineage viruses reacted poorly with antisera raised against cell-propagated B/Brisbane/60/2008, suggesting some antigenic differences.|
|90||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, 175 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 143 A(H3N2) viruses belonged to genetic group 3C.2a, 31 viruses belonged to subclade 3C.2a1 and one virus belonged to the clade 3C.3a.
Additionally, of the 54 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 45 belonged to genetic group 3C.2a and eight viruses belonged to subclade 3C.2a1. Sequencing is pending for the remaining one virus.
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
Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that all five viruses had a two amino acids deletion in the HA gene.
During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 353 influenza viruses for resistance to oseltamivir and zanamivir. All viruses were sensitive to these neuraminidase inhibitors (Table 4).
|Virus type and subtype||Oseltamivir||Zanamivir|
|# tested||# resistant (%)||# tested||# resistant (%)|
|A (H3N2)||230||0 (0%)||230||0 (0%)|
|A (H1N1)||27||0 (0%)||27||0 (0%)|
|B||96||0 (0%)||96||0 (0%)|
|TOTAL||353||0 (0%)||353||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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