FluWatch report: February 8 to February 14, 2015 (Week 6)

Influenza/ILI Activity (geographic spread)

In week 06, seven regions reported widespread activity: in MB, ON(2). QC(2), PEI and NL. Twenty-one regions reported localized activity: in AB, MB, ON(5), QC(2), NB(7), and NS(5). Twenty-two regions reported sporadic activity: in YK, NT(2), NU, BC(5), AB(4), SK(3), MB(2), QC(2), NS, and NL.  No activity was reported for eight regions: NU(2), MB, NS(3) and NF(2). Compared to the previous week, influenza activity declined overall in the Western provinces while influenza activity increased or remained similar in the Central and Atlantic provinces.

Influenza and Other Respiratory Virus Detections

In week 06, the number of positive influenza tests (1,625) and the percentage positive for influenza A (16.3%) continued to decline from the previous week The percentage of positive influenza B tests continued to increase and was 3.6 % in week 06, the highest this season thus far  (Figure 2).  In week 06, influenza B accounted for 33%-52% of influenza detections in AB, SK and QC. To date, 95% of influenza detections have been influenza A, and 99.7% of those subtyped have been A(H3N2) (Table 1). To date this season, detailed information on age and type/subtype has been received for 28,650 cases. A significantly greater proportion of laboratory detections of influenza have been reported in adults ≥65 years of age (61%) this season (Table 2) compared to the 2013-14 season when only 15.6% of cases were in adults ≥65 years of age.

In week 06, the number of positive respiratory syncytial virus (RSV) tests decreased to 914 RSV detections and remains the second most frequently detected virus after influenza (figure 3). In week 06, the percent positive for RSV detections were highest in the Prairies and has surpassed the percent positive for influenza detections in those regions. Detections of RSV since week 38 have been higher than in the previous season. Detections of all other respiratory viruses except human metapneumovirus decreased in week 06. Detections of respiratory viruses (other than RSV) have generally been lower this season compared to the previous season.

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

Antiviral Resistance

During the 2014-2015 influenza season, the NML has tested 575 influenza viruses for resistance to oseltamivir and 574 influenza viruses for resistance to zanamivir and all were sensitive to both agents. A total of 856 (99.9%) influenza A viruses were resistant to amantadine (Table 3).

Influenza Strain Characterizations

During the 2014-2015 influenza season, the National Microbiology Laboratory (NML) has characterized 194 influenza viruses [95 A(H3N2), 2 A(H1N1) and 97 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assay (n=95), one virus was antigenically similar to A/Texas/50/2012, five showed reduced titers to A/Texas/50/2012 and 89 were antigenically similar to A/Switzerland/9715293/2013, which is the influenza A(H3N2) component recommended for the 2015 Southern Hemisphere influenza vaccine. Additionally, 686 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 684 belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012.
Influenza A(H1N1): Two A(H1N1) viruses characterized were antigenically similar to A/California/7/2009.
Influenza B: Of the 97 influenza B viruses characterized, 90 viruses were antigenically similar to B/Massachusetts/2/2012, three viruses showed reduced titers against B/Massachusetts/2/2012, and four were B/Brisbane/60/2008-like (Figure 4).

Influenza-like Illness (ILI) Consultation Rate

The national influenza-like-illness (ILI) consultation rate decreased to 44.5 consultations per 1,000, which is slightly above expected levels for week 06 (Figure 5). The rate was highest among the 5 to 19 years of age group (60.1 consultations per 1,000) and lowest among the adults ≥65 years of age (36.2 consultations per 1,000)

Influenza Outbreak Surveillance

In week 06, 74 new outbreaks of influenza were reported, which is slightly higher than the number of outbreaks reported in the previous week. The majority of the outbreaks occurred in the Central and Atlantic provinces. Sixty outbreaks were reported in long-term care facilities (LTCF), four in hospitals and 10 in institutional or community settings  (Figure 6). An additional five outbreaks of ILI were reported in schools. Among the outbreaks in which the influenza subtype was known, four LTCF outbreaks were associated with A(H3N2) and five outbreaks were associated with influenza B. To date this season, 970 outbreaks in LTCFs have been reported and the majority of those with known subtypes were attributable to A(H3N2). There has been a higher number of reported influenza outbreaks to date this season compared to the same period in previous seasons.

Pharmacy surveillance

During week 06, the proportion of prescriptions for antivirals increased slightly to 298.1 antiviral prescriptions per 100,000 total prescriptions (from 289.9 per 100,000). The rate for antivirals since week 48 has been higher than the previous three seasons (Figure 7). The rate in infants and seniors increased in week 06, while the rate in children and adults decreased. The rate was highest amongst seniors at 527.0 per 100,000 total prescriptions and lowest among infants at 135.4 per 100,000 total prescriptions.

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 06, 14 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network: seven cases of influenza A and seven cases of influenza B (Figure 8a). Among the reported cases, six (43%) were <2 years of age, seven (50%) were 2 to 9 years of age and one (7%) was 10-16 years of age. One case was admitted to the ICU. To date this season, 503 hospitalizations have been reported by the IMPACT network, 465 (93%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 99% (142/144) were A(H3N2)  (Table 4).  To date, 57 cases were admitted to the ICU, of which 35 (61%) were 2 to 9 years of age (Figure 9a). Three deaths have been reported.

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 06, 56 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. Among the cases in week 06, 41 cases (73%) were in adults over the age of 65 and 46 cases (82%) had influenza A (Figure 8b).  To date this season, 1,628 cases have been reported; 1,590 (98%) with influenza A. The majority of cases (83%) were among adults ≥65 years of age (Table 5). One hundred and nineteen ICU admissions have been reported and 89 cases were adults ≥65 years of age. A total of 86 ICU cases (72%) reported to have at least one underlying condition or comorbidity. Of the 82 ICU cases with known immunization status, 30 (37%) reported not having been vaccinated this season. Seventy-four deaths have been reported, 67 (91%) of the deaths were adults >65 years of age (Figure 9B).

Note: The number of hospitalizations reported through PCIRN 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 06, 264 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *} which is less than the number reported in week 05 (n=292). Of the 264 hospitalizations, all but two were influenza A, and 77% were in patients ≥65 years of age. Since the start of the 2014-15 season, 4,817 hospitalizations have been reported; 4,715 (98%) with influenza A. Among cases for which the subtype of influenza A was reported, 99.7% were A(H3N2). The majority of cases (72%) were ≥65 years of age (Table 6). A total of 237 ICU admissions have been reported to date: 55% (130) were in adults ≥65 years of age and 30%(73) were in adults 20-64 years. A total of 342 deaths have been reported since the start of the season: four children <5 years of age, one child 5-19 years, 24 adults 20-64 years, and 313 adults ≥65 years of age. Adults 65 years of age or older represent 92% of all deaths reported this season. 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, no new laboratory-confirmed cases of human infection with avian influenza A(H7N9) virus were reported by the World Health Organization. Globally to February 19, 2015, the WHO reported a total of 571 laboratory-confirmed human cases with avian influenza A(H7N9) virus, including 204 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)

Influenza A(H5N6): Since the last FluWatch report, no new cases of human infection with avian influenza A (H5N6) virus from China has been reported by the World Health Organization. Globally to February 19, 2015, the WHO has been informed of a total of three cases of avian influenza A (H5N6) virus, including two deaths.

Middle East Respiratory Syndrome Coronavirus (MERS-CoV)
Since the last FluWatch report, 6 new laboratory-confirmed cases of MERS-CoV have been reported by the World Health Organization. Globally, from September 2012 to February 19, 2015, the WHO has been informed of a total of 983 laboratory-confirmed cases of infection with MERS-CoV, including 360 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) and for the latest global risk assessment posted by the WHO on February 5, 2015: WHO MERS-CoV.

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 11 commercial infected premises and one non-commercial infected premise with H5N2.

On February 7, 2015 an additional non-commercial farm in the Fraser Valley was confirmed to be infected with highly pathogenic avian influenza H5N1. The CFIA applies the same disease control measures following detections of H5N1 and H5N2. The infected premise is under quarantine, depopulation of the affected birds has been completed and disposal measures are underway. The CFIA has now reduced the size of the restricted zone as progress continues to be made in the control of avian influenza in British Columbia. Avian influenza viruses do not pose risks to food safety when poultry and poultry products are properly handled and cooked. Further information on the outbreak is provided on the following CFIA website.

• CFIA - Notifiable Avian Influenza

For the latest Travel Health Notice on Avian Influenza (H5N1) visit the following webpage: PHAC - Travel Health Notice.

Enterovirus D68 (EV-D68)
A summary of surveillance information on hospitalized paediatric cases of EV-D68 in September 2014 from participating jurisdictions in Canada is scheduled for publication in the Canada Communicable Disease Report (CCDR) on Feb. 20, 2015. The report can be accessed in the CCDR webpage.

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

• Non-polio enterovirus infections

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.

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