FluWatch report: November 19, 2017 to November 25, 2017 (week 47)
- At the national level, the influenza season began early this year, especially illnesses due to influenza B. Influenza activity continues to increase steadily.
- The number and percentage of laboratory tests positive for influenza continues to increase, and is higher for this time of year compared to previous seasons.
- The majority of influenza detections continue to be A(H3N2) although an elevated number of influenza B detections has also been reported.
- The number of influenza-related hospitalizations among adults, primary care consultations for influenza-like illness, and the proportion of regions reporting sporadic activity are above the expected levels for this time of year.
- 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 47, six regions in Alberta (2) and Ontario (4) reported localized activity, and 26 regions (British Columbia (5), Alberta (3), Saskatchewan (3), Manitoba (3), Ontario (3), Quebec (6), New Brunswick (1), Prince Edward Island (1), and Yukon (1)) reported sporadic activity. Consistent with the increased number of influenza detections this season, a greater number of regions are reporting sporadic activity compared to previous seasons.
Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2017-47
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
The 2017-18 season has begun early. In week 47, both influenza A and B detections continued to increase, with 10.7% of tests positive. The number and percentage of influenza A for week 47 are slightly higher than in previous seasons, although the cumulative number of detections this season remains higher compared to the previous seven seasons. The number and percentage of tests positive for influenza B remains significantly higher for this time of year compared to the same period during the previous seven seasons, with 2.3% of tests positive in week 47. 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 2017-47
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, 2,080 laboratory-confirmed influenza detections have been reported, of which 84% 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 2017-47
To date this season, detailed information on age and type/subtype has been received for 1,838 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 44% have been reported in adults 65 years of age and older. This proportion was higher among cases of influenza A(H3N2) (54%) compared to influenza B (31%).
|Age groups (years)||Cumulative (August 27, 2017 to November 25,2017)|
|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 47, 2.3% of visits to healthcare professionals were due to influenza-like illness; 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 2017-47
Number of participants reporting in week 47: 107
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 47, 1,379 participants reported to FluWatchers, of which 2% reported symptoms of cough and fever, and 25% of these consulted a healthcare professional. Among participants who reported cough and fever, 63% reported days missed from work or school, resulting in a combined total of 57 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 Facilities||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 47, seven new laboratory-confirmed influenza outbreaks were reported: two in long-term care facilities, and five in other settings. Among those with influenza type/subtype reported, five were associated with influenza A and two with influenza B.
To date this season, 41 influenza/ILI outbreaks have been reported, of which 13 (32%) occurred in LTC facilities. Among the 34 outbreaks for which the influenza type/subtype was reported, 26 were associated with influenza A (of which 20 were A(H3N2) and the others were not unsubtyped), seven were associated with influenza B, and one was associated with a mix of A(H3N2) and B. The number of outbreaks to date is within the expected range for this time of year.
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2017-47
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
In week 47, 34 influenza-associated hospitalizations were reported by participating provinces and territoriesfigure 6 note 1.
To date this season, 371 influenza-associated hospitalizations have been reported, 92% of which were associated with influenza A, and 270 cases (73%) 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. Twenty-one ICU admissions and eight 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 2017-47
- 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 47, 11 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. In weeks 46 and 47, the number of weekly hospitalizations is above the seven-season average for this week.
To date this season, 41 pediatric hospitalizations have been reported by the IMPACT network, 35 of which were associated with influenza A. Nine ICU admissions and fewer than five deaths have been reported. Compared to recent influenza A(H3N2) seasons at week 47, the number of hospitalizations reported this season has been greater than the 2016-17 season 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 2017-47
Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2017-47
Influenza Strain Characterizations
During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 103 influenza viruses [84 A(H3N2), 6 A(H1N1)pdm09 and 13 B viruses] that were received from Canadian laboratories.
Among influenza viruses characterized by hemagglutination inhibition assay during the 2017-18 season, all 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||14||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||6||Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.|
|2||Viruses antigenically similar to B/Brisbane/60/2008, the influenza B component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.|
|11||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, 70 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 51 A(H3N2) viruses belonged to genetic group 3C.2a and 19 viruses belonged to subclade 3C.2a1.
Additionally, of the 14 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 11 belonged to genetic group 3C.2a and two viruses belonged to subclade 3C.2a1. Sequencing is pending for the remaining one 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.
During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 109 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)||90||0 (0%)||90||0 (0%)|
|A (H1N1)||6||0 (0%)||6||0 (0%)|
|B||13||0 (0%)||13||0 (0%)|
|TOTAL||109||0 (0%)||109||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
- World Health Organization influenza update
- World Health Organization FluNet
- WHO Influenza at the human-animal interface
- Centers for Disease Control and Prevention seasonal influenza report
- European Centre for Disease Prevention and Control - epidemiological data
- South Africa Influenza surveillance report
- New Zealand Public Health Surveillance
- Australia Influenza Report
- Pan-American Health Organization Influenza Situation Report
- Alberta Health - Influenza Surveillance Report
- BC - Centre for Disease Control (BCCDC) - Influenza Surveillance
- New Brunswick - Influenza Surveillance Reports
- Newfoundland and Labrador - Surveillance and Disease Reports
- Nova Scotia - Flu Information
- Public Health Ontario - Ontario Respiratory Pathogen Bulletin
- Quebec - Système de surveillance de la grippe
- Manitoba - Epidemiology and Surveillance - Influenza Reports
- Saskatchewan - influenza Reports
- PEI - Influenza Summary
FluWatch definitions for the 2017-2018 season
The FluWatch report is compiled from a number of data sources. Surveillance information contained in this report is a reflection of the surveillance data available to FluWatch at the time of production. Delays in reporting of data may cause data to change retrospectively
Influenza/Influenza-like Illness (ILI) Activity
Influenza/ILI activity levels, as represented on the map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, primary care consultations for ILI and reported outbreaks. ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls, and the detemination of an increase is based on the assessment of the provincial/territorial epidemiologist. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.
Influenza/ILI activity level
1 = No activity: no laboratory-confirmed influenza detections in the reporting week, however, sporadically occurring ILI may be reported
2 = Sporadic: sporadically occurring ILI and lab confirmed influenza detection(s) with no outbreaks detected within the influenza surveillance region Footnote †
3 = Localized:
- evidence of increased ILIFootnote * and
- lab confirmed influenza detection(s) together with
- outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance regionFootnote †
4 = Widespread:
Laboratory-Confirmed Influenza Detections
Provincial, regional and some hospital laboratories report the weekly number of tests and detections of influenza and other respiratory viruses. Provincial public health laboratories submit demographic information for cases of influenza. This case-level data represents a subset of influenza detections reported through aggregate reporting. Specimens from NT, YT, and NU are sent to reference laboratories in the provinces for testing. Cumulative data includes updates to previous weeks. Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.
Syndromic/Influenza-like Illness Surveillance
FluWatch maintains a network of primary care practitioners who report the weekly proportion of ILI cases seen in their practice. Independent sentinel networks in BC, AB, and SK compile their data for reporting to FluWatch. Not all sentinel physicians report every week.
Definition of Influenza-like-illness (ILI): Acute onset of respiratory illness with fever and cough and with one or more of the following - sore throat, arthralgia, myalgia, or prostration which is likely due to influenza. In children under 5 years of age, gastrointestinal symptoms may also be present. In patients under 5 or 65 years and older, fever may not be prominent.
Influenza Outbreak Surveillance
Outbreaks of influenza or ILI are reported from all provinces and territories, according to the definitions below. However, reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions. All provinces and territories with the exception of NU report influenza outbreaks in long-term care facilities. All provinces and territories with the exception of NU and QC report outbreaks in hospitals.
Schools: Greater than 10% absenteeism (or absenteeism that is higher (e.g. >5-10%) than expected level as determined by school or public health authority) which is likely due to ILI.
Hospitals and residential institutions: two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case of influenza. Residential institutions include but are not limited to long-term care facilities (LTCF) and prisons.
Workplace: Greater than 10% absenteeism on any day which is most likely due to ILI.
Other settings: two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case of influenza; i.e. closed communities.
Serious Outcome Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
Influenza-associated hospitalizations and deaths are reported by 8 Provincial and Territorial Ministries of Health (excluding BC, NU, ON and QC). The hospitalization or death does not have to be attributable to influenza, a positive laboratory test is sufficient for reporting. Only hospitalizations that require intensive medical care are reported by SK.
Due to changes in participating provinces and territories, comparisons to previous years should be done with caution.
Pediatric Influenza Hospitalizations and Deaths
The Immunization Monitoring Program Active (IMPACT) network reports the weekly number of hospitalizations with influenza among children admitted to one of the 12 participating paediatric hospitals in 8 provinces. These represent a subset of all influenza-associated pediatric hospitalizations in Canada.
Influenza Strain Characterizations and Antiviral Resistance
Provincial public health laboratories send a subset of influenza virus isolates to the National Microbiology Laboratory for strain characterization and antiviral resistance. These represent a subset of all influenza detections in Canada and the proportion of isolates of each type and subtype is not necessarily representative of circulating viruses.
Antigenic strain characterization data reflect the results of hemagglutination inhibition (HI) testing compared to the reference influenza strains recommended by WHO. Genetic strain characterization data are based on analysis of the sequence of the viral hemagglutinin (HA) gene.
Antiviral resistance testing is conducted by phenotypic and genotypic methods on influenza virus isolates submitted to the National Microbiology Laboratory. All isolates are tested for oseltamivir and zanamivir and a subset are tested for resistance to amantadine.
Abbreviations: Newfoundland/Labrador (NL), Prince Edward Island (PE), New Brunswick (NB), Nova Scotia (NS), Quebec (QC), Ontario (ON), Manitoba (MB), Saskatchewan (SK), Alberta (AB), British Columbia (BC), Yukon (YT), Northwest Territories (NT), Nunavut (NU).
We would like to thank all the Fluwatch surveillance partners who are participating in this year's influenza surveillance program.
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