FluWatch report: April 9 – April 15, 2017 (week 15)
- Overall, influenza activity continues to decline slowly in Canada.
- In week 15, influenza B activity surpassed influenza A activity, with 50% or more of influenza laboratory detections, hospitalizations and outbreaks associated with influenza B.
- In keeping with the predominant circulation of A(H3N2) this season, the majority of laboratory detections, hospitalizations and deaths have been among adults aged 65+ years.
- 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
- 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 Activity (geographic spread)
In week 15, ten regions across six provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 27 regions across nine provinces and territories. Localized activity was reported in 15 regions across five provinces. One region in QC reported widespread activity in week 15. For more details on a specific region, click on the map.
Laboratory Confirmed Influenza Detections
In week 15, the number (582) and the percentage of tests positive for influenza (12%) decreased slightly from the previous week. The proportion of detections due to influenza B has been steadily increasing since mid-February and reached 50% in week 15. However, the number of influenza B detections remains low compared to the same time period in recent seasons, and declined slightly compared to the previous week. For data on other respiratory virus detections, see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada (PHAC) website.
Figure 2 – Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2016-17, week 15
The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the start and end of seasonal influenza activity.
To date this season, 36,542 laboratory confirmed influenza detections have been reported, of which 93% have been influenza A. Influenza A(H3N2) is the most common subtype detected. 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, 2016-17, week 15
To date this season, detailed information on age and type/subtype has been received for 25,251 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for half of the reported influenza cases. Among cases of influenza A(H3N2), adults aged 65+ represented 49% of cases, followed by adults aged 20-64 (32% of cases). Among cases of influenza B, adults aged 20-64 represented 41% of cases.
|Age groups (years)||Week (April 9, 2017 to April 15, 2017)||Cumulative (August 28, 2016 to April 15, 2017)|
|Influenza A||B||Influenza A||B||Influenza A and B|
|A Total||A(H1) pdm09||A(H3)||ATable 1 - Footnote UnS||Total||A Total||A(H1) pdm09||A(H3)||ATable 1 - Footnote UnS||Total||#||%|
|PercentageTable 1 - Footnote 2||51%||0%||8%||92%||49%||93%||0%||47%||53%||7%|
Syndromic/Influenza-like Illness Surveillance
Healthcare Professionals Sentinel Syndromic Surveillance
In week 15, 0.9% of visits to healthcare professionals were due to influenza-like illness, a decrease compared to the percentage of visits reported in week 14.
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 15
Number of participants reporting in week 15: 107
Delays in the reporting of data may cause data to change retrospectively. In BC, AB, and SK, data are compiled by a provincial sentinel surveillance program for reporting to FluWatch. Not all sentinel physicians report every week.
Are you a primary healthcare practitioner (General Practitioner, Nurse Practitioner or Registered Nurse) interested in becoming a FluWatch sentinel?
Please visit our Influenza Sentinel page for more details.
Influenza Outbreak Surveillance
In week 15, 21 laboratory confirmed influenza outbreaks were reported, slightly more compared to the previous week. Of the 14 outbreaks with known strains or subtypes: seven were due to to influenza A and seven to influenza B. One additional outbreak due to ILI was reported in a school.
To date this season, 1,107 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 56 outbreaks (7%) due to influenza B have been reported. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,646 outbreaks were reported, of which 74% occurred in LTC facilities and 81 outbreaks (5%) were due to influenza B.
Figure 5 - Text Description
|Report week||Hospitals||Long Term Care Facilities||Other|
Provincial/Territorial Influenza Hospitalizations and Deaths
In week 15, 101 influenza-associated hospitalizations were reported by participating provinces and territories*, a decrease from 146 reported in the previous week. The weekly percentage of influenza B associated hospitalizations has been steadily increasing since week 02, and in week 15, 57% of hospitalizations were associated with influenza B. The largest proportion of hospitalizations was among adults aged 65+ years (66%). Seven intensive care unit (ICU) admissions and three deaths were reported in week 15.
To date this season, 5,891 hospitalizations have been reported, of which 93% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (3064/3088) were influenza A(H3N2). Adults 65+ accounted for 68% of the hospitalizations. A total of 225 ICU admissions and 336 deaths have been reported. The majority of deaths (86%) were reported in adults aged 65+ years.
|Age Groups (years)||Cumulative (August 28, 2016 to April 15, 2017)|
|Influenza A Total||Influenza B Total||Total [# (%)]||Influenza A and B Total||%||Influenza A and B Total||%|
|0-4||435||43||478 (8%)||15||7%||<5||Table 2 - Footnote x%|
|5-19||233||45||278 (5%)||13||6%||<5||Table 2 - Footnote x%|
Sentinel Hospital Influenza Surveillance
Pediatric Influenza Hospitalizations and Deaths
In week 15, 9 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network, which is less than the previous week. Influenza B accounted for half of the cases in week 15. The number of weekly hospitalizations reported since week 05 has been below the six year average for the same time period (Figure 7).
To date this season, 506 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 39% of hospitalizations and influenza A accounted for 86% of the reported hospitalizations. Among the 69 hospitalizations due to influenza B, 33 (48%) were in children over the age of 5 years. In comparison, children over the age of 5 years accounted for 33% of influenza A hospitalizations. Additionally, 85 intensive care unit (ICU) admissions have been reported. Children aged 0-23 months accounted for 27% of ICU cases, and children aged 10-16 years for 29%. A total of 56 ICU cases (72%) reported at least one underlying condition or comorbidity. Less than five deaths have been reported this season.
Figure 6 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2016-17, week 15
Figure 6 - Text Description
Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 15
The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2015-16.
The number of hospitalizations reported through IMPACT represents a subset of all influenza-associated pediatric and adult hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.
Figure 7 - Text Description
Adult Influenza Hospitalizations and Deaths
In week 15, 29 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). The proportion of hospitalizations associated with influenza B continues to increase and was 69% in week 15. The majority of cases (79%) occurred in adults aged 65+.
To date this season, 1,453 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 94% of hospitalizations. Adults aged 65+ accounted for 79% of hospitalizations. To date, 103 intensive care unit (ICU) admissions have been reported. A total of 77 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 69 years. Approximately 68 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 85 years.
Figure 8 - Cumulative numbers of adult hospitalizations (≥20 years of age) with influenza by type and age-group reported by CIRN, Canada, 2016-17, week 15
Figure 9 – Percentage of hospitalizations, ICU admissions and deaths with influenza by age-group (≥20 years of age) reported by CIRN, Canada 2016-17, week 15
The number of hospitalizations reported through CIRN represents a subset of all influenza-associated adult hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.
Influenza Strain Characterizations
During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,669 influenza viruses [1431 A(H3N2), 36 A(H1N1), 202 influenza B]. All but one influenza A virus (n=1430) and 46 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. One hundred and fifty-six influenza B viruses were similar to the strain which is only included in the quadrivalent vaccine.
|Strain Characterization ResultsTable 3 - Footnote 1||Count||Description|
|Influenza A (H3N2)|
|348||Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine.|
|GeneticallyTable 3 - Footnote 2
Viruses belonging to genetic group 3C.2a. A/Hong Kong/4801/2014-like virus belongs to genetic group 3C.2a and is the influenza A(H3N2) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine.
Additionally, genetic characterization of the 348 influenza A (H3N2) viruses that underwent HI testing determined that 287 viruses belonged to genetic group 3C.2a and 61 viruses belonged to genetic group 3C.3a. The majority of viruses belonging to genetic group 3C.3a are inhibited by antisera raised against A/Hong Kong/4801/20143Table 3 - Footnote 3.
A/Indiana/10/2011-likeTable 3 - Footnote 4
Viruses antigenically similar to A/Indiana/10/2011, a candidate H3N2v vaccine virus.
|Influenza A (H1N1)|
|A/California/7/2009-like||36||Viruses antigenically similar to A/California/7/2009, the A(H1N1) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine influenza vaccine.|
|46||Viruses antigenically similar to B/Brisbane/60/2008, the influenza B component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent influenza vaccine|
|156||Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2016-17 Northern Hemisphere quadrivalent influenza vaccine.|
During the 2016-17 season, the National Microbiology Laboratory (NML) has tested 932 influenza viruses for resistance to oseltamivir, 884 influenza viruses for resistance to zanamivir and 208 influenza viruses for resistance to amantadine. All but two influenza A(H3N2) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir. All 208 influenza A viruses were resistant to amantadine (Table 4).
|Virus type and subtype||Oseltamivir||Zanamivir||Amantadine|
|# tested||# resistant (%)||# tested||# resistant (%)||# tested||# resistant (%)|
|A (H3N2)||717||2 (0.3%)||697||0 (0%)||178||178 (100%)|
|A (H3N2v)||1||0 (0%)||1||0 (0%)||1||1 (100%)|
|A (H1N1)||35||0 (0%)||33||0 (0%)||29||29 (100%)|
|B||179||0 (0%)||153||0 (0%)||N/ATable 4 - Footnote *||N/ATable 4 - Footnote *|
|TOTAL||932||2 (0.2%)||884||0 (0%)||208||208 (100%)|
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.
- 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.
- 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:
- 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:
- 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 greater than or equal to 50% of the influenza surveillance regionFootnote †
Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.
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