FluWatch report: December 18 to December 31, 2016 (weeks 51 and 52)

Overall Summary

• Seasonal influenza activity continues to increase in Canada, with greater numbers of influenza detections, hospitalizations and outbreaks being reported in weeks 51 and 52.
• A total of 1,948 positive influenza detections were reported in week 52. Influenza A(H3N2) continues to be the most common subtype detected.
• Seventy-one laboratory-confirmed influenza outbreaks were reported in week 52, with the majority occurring in long-term care facilities.
• Adults aged 65+ years accounted for the largest proportion of hospitalizations and deaths reported from adult sentinel networks and participating Provinces and Territories.
• Influenza activity started early this season, but so far activity has been lower than the 2014-15 season when A(H3N2) was the predominant subtype.
• For more information on the flu, see our Flu (influenza) web page.

On this page

• Influenza/Influenza-like Illness (ILI) Activity (geographic spread)
• Laboratory Confirmed Influenza Detections
• Syndromic/Influenza-like Illness Surveillance
• Influenza Outbreak Surveillance
• Provincial/Territorial Influenza Hospitalizations and Deaths
• Sentinel Hospital Influenza Surveillance
• Influenza Strain Characterizations
• Antiviral Resistance
• Provincial and International Influenza Reports
• FluWatch definitions for the 2016-2017 season

Influenza/Influenza-like Illness (ILI) Activity (geographic spread)

In week 52, a total of 18 regions in Canada reported no influenza activity. Sporadic influenza activity was reported in 19 regions across all provinces and territories except QC and SK. Localized activity was reported in 13 regions across four provinces (ON, SK, AB and BC). Widespread activity was reported in three regions (one each in SK, AB and BC). For more details on a specific region, click on the map.

Laboratory Confirmed Influenza Detections

The percentage of tests positive for influenza increased from 16% in week 51 to 24% in week 52. Compared to the previous influenza A(H3N2)-predominant season in 2014-15, the percent positive in week 52 (24%) was lower than the percent positive reported in week 52 of the 2014-15 season (34%). For data on other respiratory virus detections, see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada (PHAC) website.

Nationally in week 52, 1,948 positive influenza tests were reported, up from 1,229 tests reported in week 51. To date, a total of 6,180 laboratory confirmed influenza detections have been reported. Influenza A(H3N2) is the most common subtype detected, representing 99% of subtyped influenza A detections (3812/3835). 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.

To date this season, detailed information on age and type/subtype has been received for 5,008 laboratory confirmed influenza cases. Adults aged 65+ were the age group that accounted for the largest proportion of reported influenza cases (>45%) and the largest proportion of influenza A (H3N2) cases. Compared to the cases reported in the 2014-15 season at week 52, adults aged 65+ account for a smaller proportion of cases this season (approximately 45% in 2016-17 compared to 62% in 2014-15). Adults aged 45-64 account for a greater proportion of cases this season (approximately 23% in 2016-17 compared to 12% in 2014-15).

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 52, 3.4% of visits to healthcare professionals were due to ILI, up from week 51 where 2.0% of visits were due to ILI.

Influenza Outbreak Surveillance

In week 52, 71 laboratory confirmed influenza outbreaks were reported: 49 in long-term care (LTC) facilities, five in hospitals and 17 in institutional or community settings. Of the outbreaks with known strains or subtypes: 57 outbreaks were due to influenza A of which 17 were due to influenza A(H3N2) (15 in LTC facilities and two in institutional or community settings), 40 were due to influenza A(UnS) (24 in LTC facilities, three in hospitals and 13 in institutional or community settings) and one was due to influenza B (in a LTC facility).

To date this season, 206 outbreaks have been reported and the majority (67%) have occurred in LTC facilities. In comparison at week 52 in the 2014-15 season, the previous influenza A(H3N2)-predominant season, 457 outbreaks were reported, of which 76% occurred in LTC facilities.

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 52, 185 influenza-associated hospitalizations were reported by participating provinces and territories^{Footnote *}. Influenza A accounted for all but two of the reported hospitalizations. Adults aged 65+ accounted for the largest proportion of hospitalizations (72%).

To date this season, 892 hospitalizations have been reported, of which 98% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (576/578) were influenza A(H3N2). Adults 65+ accounted for approximately 66% of the hospitalizations. Thirty-two intensive care unit (ICU) admissions and 20 deaths have been reported. The majority of deaths (80%) were reported in adults aged 65+ years.

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In weeks 51 and 52, a total 48 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All but one case was due to influenza A. The number of hospitalizations reported in week 51 and 52 were below the six-year average number of hospitalizations for those weeks.

To date this season, 117 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-2 years accounted for approximately 36% of hospitalizations. Influenza A accounted for 89% (n=104) of the reported hospitalizations, of which 53% (n=55) were influenza A(H3N2) and the remainder were A(UnS). Additionally, 18 intensive care unit (ICU) admissions have been reported, of which 67% were reported in children aged five years and older. No deaths have been reported this season.

Compared to 2014-15, the previous influenza A(H3N2)-predominant season, where 262 hospitalizations were reported as of week 52, there has been approximately half the number of cases reported to date in the current season.

Adult Influenza Hospitalizations and Deaths

In weeks 51 and 52, a total of 151 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). All but two cases were due to influenza A and the greatest proportion of cases (67%) occurred in adults aged 65+.

To date this season, 209 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. All but two hospitalized cases were due to influenza A. Adults aged 65+ accounted for approximately 68% of hospitalizations. To date, greater than nine ICU admissions and less than five deaths have been reported.

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 199 influenza viruses [175 A(H3N2), 7 A(H1N1), 17 influenza B]. All but one influenza A virus (n=174) and 9 influenza B viruses characterized were antigentically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Eight influenza B viruses were similar to the strain which is included only in the quadirvalent vaccine.

Antiviral Resistance

During the 2016-17 season, the National Microbiology Laboratory (NML) has tested 182 influenza viruses for resistance to oseltamivir and zanamivir and 89 influenza viruses for resistance to amantadine. All viruses were sensitive to oseltamivir and zanamivir. All 89 influenza A viruses were resistant to amantadine (Table 4).

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 2016-2017 season

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).

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, gastrointestinal symptoms may also be present. In patients under 5 or 65 and older, fever may not be prominent.

ILI/Influenza outbreaks

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.
Note: it is recommended that ILI school outbreaks be laboratory confirmed at the beginning of influenza season as it may be the first indication of community transmission in an area.

Hospitals and residential institutions:

two or more cases of ILI within a seven-day period, including at least one laboratory confirmed case. Institutional outbreaks should be reported within 24 hours of identification. Residential institutions include but 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; i.e. closed communities.

Note that reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions.

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:

1. evidence of increased ILI^{Footnote *} and
2. lab confirmed influenza detection(s) together with
3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance region^{Footnote †}

4 = Widespread:

1. evidence of increased ILI^{Footnote *} and
2. lab confirmed influenza detection(s) together with
3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in greater than or equal to 50% of the influenza surveillance region^{Footnote †}

Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.