FluWatch report: March 20 to March 26, 2016 (week 12)
- For the second consecutive week, influenza activity continued to decrease across Canada.
- All regions of Canada reported sporadic or localized influenza activity.
- The number of positive influenza B tests reported continues to increase, but still accounted for only 30% of positive influenza tests in week 12
- Adults greater than 65 years of age accounted for the majority of hospitalizations in week 12 and account for the largest proportion of hospitalizations to date this season.
- Hospitalizations, ICU admissions and deaths among the pediatric population, while declining, remain above expected levels based on the past several influenza seasons.
- For more information on the flu, see our Flu(influenza) web page.
Are you a primary health care practitioner (General Practitioner, Nurse Practitioner or Registered Nurse) interested in becoming a FluWatch sentinel for the 2015-16 influenza season? Contact us at FluWatch@phac-aspc.gc.ca
On this page
- Influenza/ILI Activity (geographic spread)
- Laboratory Confirmed Influenza Detections
- Influenza-like Illness Consultation Rate
- Pharmacy Surveillance
- Influenza Outbreak Surveillance
- Sentinel Pediatric Hospital Influenza Surveillance
- Provincial/Territorial Influenza Hospitalizations and Deaths
- Influenza Strain Characterizations
- Antiviral Resistance
- International Influenza Reports
- FluWatch definitions for the 2015-2016 season
Influenza/Influenza-like Illness Activity (geographic spread)
In week 12, influenza activity was present in all regions of Canada. A total of 21 regions reported localized activity levels across the country. Sporadic influenza/ILI activity was reported in 32 regions across Canada.
Laboratory Confirmed Influenza Detections
In week 12, the percent positive for influenza continued to decrease from the previous week [from 31% in week 11 to 30% in week 12 (Figure 2)]. Compared to the previous five seasons, the percent positive (30%) reported in week 12 was above the five year average for that week and exceeded the expected levels (range 11.3%-19.8%). With the late start to the 2015-16 influenza season, these above normal levels are not unexpected.
In week 12, there were 2,882 positive influenza tests reported. To date, 81% of influenza detections have been influenza A and among those subtyped, the vast majority have been influenza A(H1N1) [91% (9630/10584]. The number of positive influenza B tests reported is accounting for an increasing proportion of all positive influenza tests reported; this week, influenza B positive tests accounted for 30% of all positive tests.
Figure 3. Cumulative numbers of positive influenza specimens by type/subtype and province, Canada, 2015-16
Note: Specimens from NT, YT, and NU are sent to reference laboratories in other provinces. Cumulative data includes updates to previous weeks.
To date this season, detailed information on age and type/subtype has been received for 24,173 cases. Adults aged 20-44 years accounted for the greatest proportion of influenza cases, followed closely by adults aged 45-64 (Table 1). Adults aged 20-44 and 45-64 years accounted for 55% of reported influenza A(H1N1) cases. Children 5-19 years and adults 20-44 years accounted for 57% of all influenza B cases reported.
|Age groups (years)||Weekly (March 20 to March 26, 2016)||Cumulative (August 30, 2015 to March 26, 2016)|
|Influenza A||B||Influenza A||B||Influenza A and B|
|A Total||A(H1) pdm09||A(H3)||A UnSTable 1 - Footnote 3||Total||A Total||A(H1) pdm09||A(H3)||A UnSTable 1 - Footnote 3||Total||#||%|
|<5||259||15||<5||Table 1 - Footnote x||112||3794||1564||62||2168||710||4511||19%|
|5-19||83||11||<5||Table 1 - Footnote x||148||2055||931||89||1035||1351||3417||14%|
|20-44||235||26||<5||Table 1 - Footnote x||122||4893||2404||138||2351||1146||6048||25%|
|45-64||303||38||<5||Table 1 - Footnote x||62||5172||2310||172||2690||521||5698||24%|
|PercentageTable 1 - Footnote 2||69%||11%||1%||88%||31%||82%||43%||4%||53%||18%|
For data on other respiratory virus detections see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada website.
Influenza-like Illness Consultation Rate
The national ILI consultation rate decreased from the previous week from 53.6 per 1,000 patient visits in week 11, to 43.6 per 1,000 patient visits in week 12.The highest ILI consultation rate was found in the 5-19 years age group (84.2 per 1,000) and the lowest was found in the ≥65 years age group (14.7 per 1,000) (Figure 4).
During week 12, the proportion of prescriptions for antivirals decreased to 72.9 antiviral prescriptions per 100,000 total prescriptions, which is slightly higher than the five year historical average for week 12. The proportion of prescriptions for antivirals remains highest among children. In week 12, the proportion reported among children was 199.3 per 100,000 total prescriptions.
Influenza Outbreak Surveillance
In week 12, 27 new laboratory confirmed influenza outbreaks were reported: 13 in long-term care facilities (LTCF), nine in hospitals and 5 in institutions or community settings. Of the outbreaks with known strains or subtypes, one outbreak was due to influenza B, three outbreaks were due to influenza A(H1N1) and three were due to influenza A(Uns). Additionally, one ILI outbreak was reported in a school.
To date this season, 330 outbreaks have been reported. At week 12 in the 2014-15 season, 1,587 outbreaks were reported and in the 2013-14 season,170 outbreaks were reported.
Figure 6. Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2015-2016
Sentinel Pediatric Hospital Influenza Surveillance
Paediatric Influenza Hospitalizations and Deaths
In week 12, 85 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network, a decrease from the previous three weeks (Figure 7). The largest proportion of hospitalizations were in children aged 5-9 years, accounting for 27% of the hospitalizations. The majority of hospitalizations were due to influenza A (65%).
To date this season, 1007 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations have been reported by the IMPACT network: 783 hospitalized cases were due to influenza A and 224 cases were due to influenza B. The greatest proportion of hosptalization cases were in children aged 6-23 months and children 2-4 years, each accounting for 28% of hospitalizations. To date, 169 intensive care unit (ICU) admissions have been reported. Children aged 2 to 4 and 5 to 9 years each accounted for 27% of ICU admissions. A total of 135 ICU cases (80%) reported to have at least one underlying condition or comorbidity. Seven influenza-associated deaths have been reported.
|Age Groups||Cumulative (30 Aug. 2015 to 26 March 2016)|
|Influenza A||Influenza B||Influenza A and B (#(%))|
|A Total||A(H1) pdm09||A(H3)||A (UnS)||B Total|
|0-5m||106||32||<5||Table 2 - Footnote x||17||123 (12%)|
|2-4y||226||75||<5||Table 2 - Footnote x||53||279 (28%)|
|5-9y||166||45||<5||Table 2 - Footnote x||73||239 (24%)|
|10-16y||52||18||<5||Table 2 - Footnote x||32||84 (8%)|
Figure 7. Number of cases of influenza reported by sentinel hospital networks, by week, Canada, 2015-16, paediatric and adult hospitalizations (≤16 years of age, IMPACT; ≥16 years of age, CIRN-SOS)
Not included in Table 2 and Figure 7 are two IMPACT cases that were due to co-infections of influenza A and B.
Adult Influenza Hospitalizations and Deaths
In week 12, 57 hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS) (Figure 7). The largest proportion of hospitalizations were in adults 65+ years of age (53%) and due to influenza A (81%).
To date this season, 791 laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations have been reported by CIRN-SOS (Table 3). The majority of hospitalized cases were due to influenza A (86%) and the largest reported proportion were among adults ≥65 years of age (48%). One hundred and twelve intensive care unit (ICU) admissions have been reported and among those, 101 (90%) were due to influenza A. A total of 69 ICU cases (62%) reported to have at least one underlying condition or comorbidity. Twenty-seven deaths have been reported this season with the majority of deaths reported in adults ≥65 years of age (67%).
|Age groups (years)||Cumulative (1 Nov. 2015 to 26 March 2016)|
|Influenza A||B||Influenza A and B|
|A Total||A(H1) pdm09||A(H3)||A(UnS)||Total||# (%)|
|20-44||106||33||<5||Table 3 - Footnote x||21||127 (16%)|
|45-64||245||69||<5||Table 3 - Footnote x||25||270 (34%)|
Figure 8. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥16 year of age), Canada 2015-16
Note: The number of hospitalizations reported through CIRN-SOS and IMPACT represents a subset of all influenza-associated adult and paediatric hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.
x - Suppressed to prevent residual disclosure.
Provincial/Territorial Influenza Hospitalizations and Deaths
Since the start of the 2015-16 season, 3,491 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 3,024 hospitalizations (87%) were due to influenza A and 467 (13%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 93% (1442/1554) were influenza A(H1N1). The largest proportion (30%) of hospitalized cases were ≥65 years of age, followed closely by adults 45-64 years of age (27%). Three hundred and eighty nine ICU admissions have been reported of which 225 (58%) were due to influenza A(H1N1) and 175 (45%) were in the 45-64 age group. A total of 140 deaths have been reported; all but 10 were associated with influenza A. Adults ≥65 years of age each represented 46% of reported deaths.
Figure 9. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group, Canada 2015-16
x - Suppressed to prevent residual disclosure.
See additional data on Reported Influenza Hospitalizations and Deaths in Canada: 2011-12 to 2015-16 on the Public Health Agency of Canada website.
Influenza Strain Characterizations
During the 2015-16 influenza season, the National Microbiology Laboratory (NML) has characterized 1312 influenza viruses [149 A(H3N2), 775 A(H1N1) and 388 influenza B].
Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 35 H3N2 virus were antigenically characterized as A/Switzerland/9715293/2013-like using antiserum raised against cell-propagated A/Switzerland/9715293/2013.
Sequence analysis was done on 114 H3N2 viruses. All viruses belonged to a genetic group for which most viruses were antigenically related to A/Switzerland/9715293/2013. A/Switzerland/9715293/2013 is the A(H3N2) component of the 2015-16 Northern Hemisphere's vaccine.
Influenza A (H1N1): A total of 775 H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.
Influenza B: A total of 104 influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. A total of 284 influenza B viruses were characterized as B/Brisbane/60/2008-like, one of the influenza B components of the 2015-16 Northern Hemisphere quadrivalent influenza vaccine.
The recommended components for the 2015-2016 northern hemisphere trivalent influenza vaccine include: an A/California/7/2009(H1N1)pdm09-like virus, an A/Switzerland/9715293/2013(H3N2)-like virus, and a B/Phuket/3073/2013 -like virus (Yamagata lineage). For quadrivalent vaccines, the addition of a B/Brisbane/60/2008-like virus (Victoria lineage) is recommended.
The NML receives a proportion of the influenza positive specimens from provincial laboratories for strain characterization and antiviral resistance testing. Characterization data reflect the results of haemagglutination inhibition testing compared to the reference influenza strains recommended by WHO.
During the 2015-16 season, the National Microbiology Laboratory (NML) has tested 904 influenza viruses for resistance to oseltamivir, 826 for resistance to zanamivir and 940 influenza viruses for resistance to amantadine. All but seven tested viruses were sensitive to oseltamivir. The seven H1N1 viruses resistant to oseltamivir had a H275Y mutation. All viruses tested for resistance were sensitive to zanamivir. All but one influenza A viruses were resistant to amantadine (Table 4).
|Virus type and subtype||Oseltamivir||Zanamivir||Amantadine|
|# tested||# resistant (%)||# tested||# resistant (%)||# tested||# resistant (%)|
|A (H3N2)||137||0||134||0||160||159 (99.4%)|
|A (H1N1)||545||7||479||0||780||780 (100%)|
|B||222||0||213||0||NATable 4 - Footnote *||NATable 4 - Footnote *|
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
FluWatch definitions for the 2015-2016 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
3 = Localized:
4 = Widespread:
Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.
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