FluWatch report: December 7 to 13, 2014 (Week 50)

Influenza/ILI Activity (geographic spread)

In week 50, four regions reported widespread activity (in AB), 17 regions reported localized activity (in BC(2), SK, MB(2), ON(5), QC(5), NS, NL), and 16 regions (in NT, YK, BC(3), AB, SK(2), MB(3), ON, QC, NB, PE, and NL) reported sporadic activity (Figure 1).

Influenza and Other Respiratory Virus Detections

In week 50, the number of positive influenza tests increased sharply for the fourth week in a row, to 1,963 influenza detections (25.9% of tests), predominantly due to influenza A (Figure 2). To date, 96% of influenza detections have been influenza A, and 99.6% of those subtyped have been A(H3) (Table 1). The timing of the season and predominant A(H3N2) subtype is similar to the pattern observed during the 2012-13 influenza season when percent positive for influenza peaked in week 52 (35%). To date, among the cases of influenza with reported age, the largest proportion was in adults ≥65 years of age (56%) (Table 2).

Detections of RSV increased sharply in week 50 and was the second most frequently detected virus, after influenza. Detections of parainfluenza and adenovirus also continue to follow their seasonal patterns of broad winter circulation. Detections of rhinovirus peaked in week 39 and continue to follow a downward trend (figure 3).

For more details, see the weekly Respiratory Virus Detections in Canada Report.

Influenza Strain Characterizations

During the 2014-2015 influenza season, the National Microbiology Laboratory (NML) has characterized 30 influenza viruses [13 A(H3N2), 2 A(H1N1) and 15 influenza B]. When tested by hemagglutination inhibition (HI) assay, one influenza A (H3N2) virus was antigenically similar to A/Texas/50/2012, two influenza A (H1N1) viruses were antigenically similar to A/California/7/2009 and 12 influenza B viruses were antigenically similar to the B/Massachusetts/2/2012 (Yamagata lineage) recommended by the WHO for the 2014-15 seasonal influenza vaccine. Five influenza A(H3N2) viruses and three influenza B viruses showed reduced titers to antisera produced against strains recommended for the seasonal influenza vaccine. Seven of the 13 influenza A (H3N2) viruses were antigenically similar to the A/Switzerland/9715293/2013, which is the influenza A/H3N2 component recommended for the 2015 Southern Hemisphere influenza vaccine (Figure 4). Additionally, 58 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 57 belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012.

Antiviral Resistance

During the 2014-2015 influenza season, NML has tested 93 influenza viruses for resistance to oseltamivir and zanamivir and all were sensitive to both agents. A total of 130 (99%) influenza A viruses tested for amantadine resistance were resistant (Table 3).

Influenza-like Illness (ILI) Consultation Rate

The national influenza-like-illness (ILI) consultation increased in week 50 to 30.91 consultations per 1,000, which is within expected levels for week 50 (Figure 5).  This week, the rates were highest among the 0 to 5 years of age group and lowest among the 5 to 19 years of age group.

Influenza Outbreak Surveillance

In week 50, 72 new outbreaks of influenza A were reported: 57 in long-term care facilities (LTCF), two in hospitals and 13 in institutional or community settings  (Figure 6). An additional six outbreaks of ILI were reported in schools. Among the outbreaks in which the influenza subtype was known, 12 LTCF outbreaks, eight institutional or community setting outbreaks, and one hospital outbreak were associated with A(H3N2). To date this season, 141 outbreaks in LTCF have been reported. The number of outbreaks reported is similar to the number reported in week 51 during the 2012-13 influenza season when influenza A(H3N2) also predominated.

Pharmacy surveillance

During week 50, the proportion of prescriptions for antivirals increased to 150.8 antiviral prescriptions per 100,000 total prescriptions, which is higher than the previous three seasons (Figure 7). The rates were highest in seniors and children (207 and 197 per 100,000 antiviral prescriptions respectively).

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 50, 38 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network: 37 cases of influenza A and one case of influenza B (Figure 8a). Among reported cases, 16 (42%) were <2 years of age, 19 (46%) were 2 to 9 years of age and three (8%) were 10-16 years of age. Three cases, all 5-9 years of age, were admitted to the ICU. To date this season, 139 hospitalizations have been reported by the IMPACT network, 125 (90%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 97% (72/74) were A(H3N2). Children <5 years of age represented 62% of cases (Table 4). To date, 12 cases were admitted to the ICU, of which 8 (67%) were 2 to 9 years of age (Figure 9a).

Note: The number of hospitalizations reported through IMPACT represents a subset of all influenza-associated paediatric hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

Adult Influenza Hospitalizations and Deaths (PCIRN)

In week 50, 60 laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations were reported by the PHAC/CIHR Influenza Research Network (PCIRN) Serious Outcomes Surveillance (SOS) network. Fifty-eight cases (97%) were influenza A (Figure 8b). To date this season, 139 cases have been reported; 137 (98.5%) with influenza A. The majority of cases (86%) were among adults ≥65 years of age (Table 5). Nine ICU admissions have been reported and the majority of cases (77.8%) were adults ≥65 years of age with underlying conditions or comorbidities. Four deaths have been reported, all adults >65 years of age (Figure 9b).

Note: 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.

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 50, 113 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *}; all but four with influenza A, and 65% were patients ≥65 years of age. Since the start of the 2014-15 season, 492 hospitalizations have been reported; 476 (97%) with influenza A. Among cases for which the subtype of influenza A was reported, 99% (374/376) were A(H3N2). The majority of cases (59%) were ≥65 years of age (Table 6). Ten ICU admissions have been reported in adults ≥65 years of age with influenza A. Twenty-seven deaths with influenza A have been reported: one child <5 years of age, one adult 45-64 years and 25 adults ≥65 years of age. Detailed clinical information (e.g. underlying medical conditions) is not known for these cases.

See additional data on Reported Influenza Hospitalizations and Deaths in Canada: 2009-10 to 2014-15 on the Public Health Agency of Canada website.

Emerging Respiratory Pathogens

Human Avian Influenza
Influenza A(H7N9): Since the last FluWatch report, 11 new laboratory-confirmed cases of human infection with avian influenza A(H7N9) virus have been reported by the World Health Organization. Globally to December 18, 2014, the WHO has been informed of a total of 469 laboratory-confirmed human cases with avian influenza A(H7N9) virus, including 182 deaths.

Documents related to the public health risk of influenza A(H7N9), as well as guidance for health professionals and advice for the public is updated regularly on the following websites:

PHAC - Avian influenza A(H7N9)
WHO - Avian Influenza A(H7N9)

Middle East Respiratory Syndrome Coronavirus (MERS-CoV)

Since the last FluWatch report, 11 laboratory-confirmed cases and 4 deaths of MERS-CoV have been reported by the World Health Organization. Globally, from September 2012 to December 18, 2014, the WHO has been informed of a total of 938 laboratory-confirmed cases of infection with MERS-CoV, including 343 deaths. All cases have either occurred in the Middle East or have had direct links to a primary case infected in the Middle East. The public health risk posed by MERS-CoV in Canada remains low (see the PHAC Assessment of Public Health Risk).

Documents related to the public health risk of MERS-CoV, as well as guidance for health professionals and advice for the public is updated regularly on the following websites:

• PHAC - Middle East respiratory syndrome coronavirus (MERS-CoV)
• WHO - Coronavirus infections

Avian Influenza A(H5)

The Canadian Food Inspection Agency (CFIA) is continuing its investigation into an outbreak of highly pathogenic avian influenza H5N2 virus in British Columbia's Fraser Valley. To date, there have been ten infected premises. As part of regular investigation activities, CFIA is fully tracing movements in and out of these sites. This may lead to further premises being identified and depopulated, which would not be unexpected. While there are no reports of H5N2 related illness in humans, as a precautionary measure public health officials are monitoring workers who are exposed to affected poultry. Avian influenza viruses do not pose risks to food safety when poultry and poultry products are properly handled and cooked. Avian influenza rarely affects humans that do not have consistent contact with infected birds. Further information on the outbreak is provided on the following CFIA.

• CFIA - Notifiable Avian Influenza

Enterovirus D68 (EV-D68)

Information related to enterovirus D68, as well as guidance for health professionals and advice for the public is updated regularly on the following website:

• PHAC – Non-polio enterovirus

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 2014-2015 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.

We would like to thank all the Fluwatch surveillance partners who are participating in this year's influenza surveillance program.