FluWatch report: March 22 to 28, 2015 (Week 12)

Influenza/ILI Activity (geographic spread)

In week 12, two regions in Quebec reported widespread activity. Twenty-two regions reported localized activity: BC, AB, MB(2), ON(7), QC(2), NB(3), NS(5) and NL. Twenty-eight regions reported sporadic activity: in YK, NT(2), BC(4), AB(4), SK(3), MB(2), QC(2), NB(4), NS(3), PE and NF(2). No activity was reported in six regions : NU(3). MB, NS, and NL.

Influenza and Other Respiratory Virus Detections

In week 12, the percentage positive for influenza A (4.7%) continued to decline from the previous week while the percentage of positive influenza B tests continued to increase (11.5%) (Figure 2). Influenza B detections were greater than influenza A in all provinces except NL. To date, 87% of influenza detections have been influenza A, and 99.3% of those subtyped have been A(H3N2) (Table 1).  To date this season, detailed information on age and type/subtype has been received for 33,953 cases (Table 2). Adults ≥65 years of age have predominantly been affected by influenza A, accounting for 62% of influenza A detections. Influenza B, while much smaller in numbers, is mainly affecting individuals less than 65 years of age, they account for 60% of influenza B detections.

In week 12, detections for all other respiratory viruses remained similar to, or decreased from, the previous week (figure 3).

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

Antiviral Resistance

During the 2014-2015 influenza season, the NML has tested 1,094 influenza viruses for resistance to oseltamivir and 1,090 influenza viruses for resistance to zanamivir. All viruses were sensitive to zanamivir and one influenza A(H3N2) virus was resistant to oseltamivir. A total of 1,235 influenza A viruses (99.9%) were resistant to amantadine (Table 3).

Influenza Strain Characterizations

During the 2014-2015 influenza season, the National Microbiology Laboratory (NML) has characterized 490 influenza viruses [176 A(H3N2), 9 A(H1N1) and 305 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assay (n=176), one virus was antigenically similar to A/Texas/50/2012, five showed reduced titers to A/Texas/50/2012 and 170 were antigenically similar to A/Switzerland/9715293/2013, which is the influenza A(H3N2) component recommended for the 2015 Southern Hemisphere influenza vaccine. Additionally, 1025 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 1023 belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012. 
Influenza A(H1N1): Nine A(H1N1) viruses characterized were antigenically similar to A/California/7/2009.
Influenza B: Of the 305 influenza B viruses characterized, 291 viruses were antigenically similar to B/Massachusetts/2/2012, three viruses showed reduced titers against B/Massachusetts/2/2012, and 14 were B/Brisbane/60/2008-like (Figure 4).

Influenza-like Illness (ILI) Consultation Rate

The national influenza-like-illness (ILI) consultation rate decreased in week 12 to 20.5 consultations per 1,000, which is below expected levels (Figure 5).

Influenza Outbreak Surveillance

In week 12, 33 new outbreaks of influenza were reported. The majority of the outbreaks occurred in the Central and Atlantic provinces. Thirty-one outbreaks were reported in long-term care facilities (LTCF) and two in institutional or community settings (Figure 6). Among the outbreaks in which the influenza type was known (n=12), eight outbreaks were associated with influenza B. To date this season, 1,173 outbreaks in LTCFs have been reported and the majority of those with known subtypes were attributable to A(H3N2). There have been a higher number of reported influenza outbreaks to date this season compared to the same period in previous seasons.

Pharmacy surveillance

During week 12, the proportion of prescriptions for antivirals decreased to 110.0 antiviral prescriptions per 100,000 total prescriptions (from 135.8 per 100,000). The rate for antivirals since week 48 has been higher than the previous three seasons (Figure 7). The rate in all age groups decreased in week 12. The rate was highest among seniors at 176.7 per 100,000 total prescriptions and lowest among infants at 10.4 per 100,000 total prescriptions.

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 12, 23 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All 23 cases were influenza B (Figure 8a). A greater proportion of cases have been reported with influenza B in recent weeks, following the trend in laboratory detections. Among the reported cases, five (22%) were <2 years of age, ten (43%) were 2 to 9 years of age and eight (35%) were 10-16 years of age. Three ICU admissions were reported.

To date this season, 621 hospitalizations have been reported by the IMPACT network, 503 (81%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 99% (162/164) were A(H3N2) (Table 4). To date, 79 cases were admitted to the ICU, of which 44 (56%) were 2 to 9 years of age (Figure 9a).  A total of 51 ICU cases reported to have at least one underlying condition or comorbidity. Four 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 12, 40 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 12, 30 cases (75%) were in adults over the age of 65 and 25 cases (63%) had influenza B (Figure 8b).  

To date this season, 2,071 cases have been reported; 1,876 (91%) with influenza A. The majority of cases (82%) were among adults ≥65 years of age (Table 5). One hundred and fifty one ICU admissions have been reported and 113 cases were adults ≥65 years of age. A total of 110 ICU cases (73%) reported to have at least one underlying condition or comorbidity. Of the 114 ICU cases with known immunization status, 38 (33%) reported not having been vaccinated this season. One hundred and twenty one deaths have been reported, 111 (92%) 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 12, 148 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *}which is similar to the number reported the previous week. Of the 148 hospitalizations, 97 (66%) were due to influenza A and 97 (65%) were in patients ≥65 years of age.

Since the start of the 2014-15 season, 6,499 hospitalizations have been reported; 6,008 (92.4%) with influenza A. Among cases for which the subtype of influenza A was reported, 99.5% were A(H3N2). The majority of cases (71%) were ≥65 years of age (Table 6). A total of 340 ICU admissions have been reported to date: 54% (n=183) were in adults ≥65 years of age and 32% (n=110) were in adults 20-64 years. A total of 479 deaths have been reported since the start of the season: three children <5 years of age, three children 5-19 years, 40 adults 20-64 years, and 433 adults ≥65 years of age. Adults 65 years of age or older represent 90% 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 April 1, 2015, the WHO reported a total of 631 laboratory-confirmed human cases with avian influenza A(H7N9) virus, including 221 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 April 1, 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, no new laboratory-confirmed cases of MERS-CoV have been reported by the World Health Organization. Globally, from September 2012 to April 1, 2015, the WHO has reported a total of 1,090 laboratory-confirmed cases of infection with MERS-CoV, including 412 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

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.