FluWatch report: April 23 – April 29, 2017 (week 17)
- Overall, influenza activity continues to decline slowly in Canada.
- In week 17, influenza B accounted for the majority of influenza activity in Canada with 50% or more of influenza laboratory detections, hospitalizations and outbreaks due to influenza B.
- This increase in influenza B activity is expected as influenza B often appears later in the flu 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 17, seven regions across four provinces and territories (NL, NS, NT and NU) reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 33 regions across 12 provinces and territories (all provinces and territories except ON). Localized activity was reported in 13 regions across four provinces (QC, ON, AB and BC). For more details on a specific region, click on the map.
Laboratory Confirmed Influenza Detections
In week 17, the number (462) and the percentage (9.8%) of tests positive for influenza decreased from the previous week. Influenza B was the most common type of influenza detected in all but two jurisdictions in Canada (QC and NS). Overall in week 17, influenza B, accounted for 66% of total detections. The number of influenza B detections remains low compared to the same time period in recent seasons. 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 17
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, 37,593 laboratory confirmed influenza detections have been reported, of which 91% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season. 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 17
To date this season, detailed information on age and type/subtype has been received for 26,007 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. Adults aged 65+ have predominantly been affected by influenza A accounting for 51% of influenza A detections. Influenza B, while much smaller in numbers is mainly affecting individuals less than 65 years of age. Individuals less than 65 years of age accounted for 67% of influenza B detections.
|Age groups (years)||Weekly (April 23 to April 29, 2017)||Cumulative (August 28, 2016 to April 29, 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||x%||x%||x%||x%||x%||91%||0%||46%||53%||9%|
Syndromic/Influenza-like Illness Surveillance
Healthcare Professionals Sentinel Syndromic Surveillance
In week 17, 0.9% of visits to healthcare professionals were due to influenza-like illness, a decrease compared to the percentage of visits reported in week 16.
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 17
Number of Sentinels Reporting Week 17: 113
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 17, 17 laboratory-confirmed influenza outbreaks were reported, an increase from the previous week. Of the 13 outbreaks with known strains or subtypes: four were due to influenza A and nine were due to influenza B.
To date this season, 1,136 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 68 outbreaks (6%) due to influenza B have been reported.
Figure 5 - Text Description
|Report week||Hospitals||Long Term Care Facilities||Other|
Provincial/Territorial Influenza Hospitalizations and Deaths
In week 17, 78 influenza-associated hospitalizations were reported by participating provinces and territories*, a decrease from 121 reported in the previous week. In week 17, 60% of hospitalizations occurred in adults 65+ and influenza B accounted for 73% of reported hospitalizations. Additionally, less than five intensive care unit (ICU) admissions and six deaths were reported.
To date this season, 6,110 hospitalizations have been reported, of which 92% were due to influenza A. Among cases for which the subtype of influenza A was reported, 99% were influenza A(H3N2). Adults 65+ accounted for 68% of the hospitalizations. A total of 242 ICU admissions and 354 deaths have been reported. The majority of deaths (88%) were reported in adults aged 65+ years.
|Age Groups (years)||Cumulative (August 28, 2016 to April 29, 2017)|
|Influenza A Total||Influenza B Total||Total [# (%)]||Influenza A and B Total||%||Influenza A and B Total||%|
|0-4||440||53||493 (8%)||16||7%||<5||Table 2 - Footnote x%|
|5-19||236||60||296 (5%)||15||6%||<5||Table 2 - Footnote x%|
Sentinel Hospital Influenza Surveillance
Pediatric Influenza Hospitalizations and Deaths
In week 17, seven laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network, of which five were associated with influenza B. Pediatric hospitalizations have been declining since the peak in early January. The number of weekly hospitalizations has been below the six year average since early February (Figure 7).
To date this season, 531 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 38% of hospitalizations and influenza A accounted for 84% of the reported hospitalizations. Among the 84 hospitalizations due to influenza B, 43 (51%) 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, 88 intensive care unit (ICU) admissions have been reported. A total of 60 ICU cases (70%) 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 17
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 17
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 17, 16 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN), unchanged from the previous week. In week 17, the majority (88%) of hospitalizations occurred in adults 65+ and influenza B accounted for 75% of reported hospitalizations.
To date this season, 1,525 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 92% of hospitalizations. Adults aged 65+ accounted for 79% of hospitalizations. To date, 134 intensive care unit (ICU) admissions have been reported. Among cases with available data, 105 ICU cases (78%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 70 years. Approximately 70 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 17
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 17
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 1,762 influenza viruses [1530 A(H3N2), 36 A(H1N1), 232 influenza B]. All but one influenza A virus (n=1529) and 54 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. One hundred and seventy-eight 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)|
|351||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 351 influenza A (H3N2) viruses that underwent HI testing determined that 288 viruses belonged to genetic group 3C.2a and 63 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/4801/2014Table 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 influenza vaccine.|
|54||Viruses antigenically similar to B/Brisbane/60/2008, the influenza B component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent influenza vaccine|
|178||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 989 influenza viruses for resistance to oseltamivir, 988 influenza viruses for resistance to zanamivir and 220 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 220 influenza A viruses were resistant to amantadine (Table 4).
|Virus type and subtype||Oseltamivir||Zanamivir||Amantadine|
|# tested||# resistant (%)||# tested||# resistant (%)||# tested||# resistant (%)|
|A (H3N2)||729||2 (0.3%)||728||0 (0%)||190||190 (100%)|
|A (H3N2v)||1||0 (0%)||1||0 (0%)||1||1 (100%)|
|A (H1N1)||35||0 (0%)||34||0 (0%)||29||29 (100%)|
|B||224||0 (0%)||225||0 (0%)||N/ATable 4 - Footnote *||N/ATable 4 - Footnote *|
|TOTAL||989||2 (0.2%)||988||0 (0%)||220||220 (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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