FluWatch report: March 15 to 21, 2015 (Week 11)

Influenza/ILI Activity (geographic spread)

In week 11, four regions reported widespread activity: QC(3) and NL. Twenty-two regions reported localized activity: BC(2), AB, MB, ON(7), QC(2), NB(3), NS(5) and PE. Twenty-four regions reported sporadic activity: in YK, NT(2), BC(3), AB(4), SK(3), MB(2), QC, NB(3), NS(3), and NF(2). No activity was reported in eight regions : NU(3). MB(2), NB, NS, and NL.

Influenza and Other Respiratory Virus Detections

In week 11, the number of positive influenza tests (958) and the percentage positive for influenza A (5.4%) continued to decline from the previous week (Figure 2). The percentage of positive influenza B tests continued to increase and was 11.5% in week 11. Influenza B detections were greater than influenza A detections in many provinces (BC, AB, SK, MB, QC, PE and NS). To date, 89% of influenza detections have been influenza A, and 99.4% of those subtyped have been A(H3N2) (Table 1). To date this season, detailed information on age and type/subtype has been received for 33,253 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, accounting for 60% of influenza B detections.

In week 11, detections for all other respiratory viruses remained similar to, or decreased from, the previous week, except those for rhinovirus (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 1,024 influenza viruses for resistance to oseltamivir and 1,021 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 1,223 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 414 influenza viruses [174 A(H3N2), 5 A(H1N1) and 235 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assay (n=174), one virus was antigenically similar to A/Texas/50/2012, five showed reduced titers to A/Texas/50/2012 and 168 were antigenically similar to A/Switzerland/9715293/2013, which is the influenza A(H3N2) component recommended for the 2015 Southern Hemisphere influenza vaccine. Additionally, 971 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 969 belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012.
Influenza A(H1N1): Five A(H1N1) viruses characterized were antigenically similar to A/California/7/2009.
Influenza B: Of the 235 influenza B viruses characterized, 225 viruses were antigenically similar to B/Massachusetts/2/2012, three viruses showed reduced titers against B/Massachusetts/2/2012, and seven 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 11 to 28.9 consultations per 1,000, which is within expected levels (Figure 5).

Influenza Outbreak Surveillance

In week 11, 63 new outbreaks of influenza were reported. The majority of the outbreaks occurred in the Central and Atlantic provinces. Forty-nine outbreaks were reported in long-term care facilities (LTCF), five in hospitals and nine in institutional or community settings  (Figure 6). An additional two outbreaks of ILI were reported in schools. Among the outbreaks in which the influenza subtype was known (n=11), ten outbreaks were associated with influenza B (one in a hospital, seven in LTCFs, and two in an institutional or community setting). To date this season, 1,142 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 11, the proportion of prescriptions for antivirals was 119.1 antiviral prescriptions per 100,000 total prescriptions which was similar to the previous week. The rate for antivirals since week 48 has been higher than the previous three seasons (Figure 7). The rate in all age groups except seniors decreased in week 11. The rate was highest among seniors at 189.5 per 100,000 total prescriptions and lowest among infants at 50.5 per 100,000 total prescriptions.

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 11, 14 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network: five cases of influenza A and nine cases of 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, three (21%) were <2 years of age, ten (71%) were 2 to 9 years of age and one (7%) was 10-16 years of age. One ICU admission was reported.

To date this season, 595 hospitalizations have been reported by the IMPACT network, 502 (84%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 99% (163/165) were A(H3N2) (Table 4).To date, 74 cases were admitted to the ICU, of which 39 (53%) were 2 to 9 years of age (Figure 9a). A total of 49 ICU cases reported to have at least one underlying condition or comorbidity. 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 11, 28 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 11, 20 cases (74%) were in adults over the age of 65 and 18 cases (67%) had influenza B (Figure 8b).  

To date this season, 2,009 cases have been reported; 1,852 (92%) with influenza A. The majority of cases (82%) were among adults ≥65 years of age (Table 5). One hundred and forty nine ICU admissions have been reported and 112 cases were adults ≥65 years of age. A total of 107 ICU cases (72%) reported to have at least one underlying condition or comorbidity. Of the 114 ICU cases with known immunization status, 37 (32%) reported not having been vaccinated this season. One hundred and seventeen deaths have been reported, 107 (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 11, 148 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *}which is slightly more than the number reported in week 10 (n=139). Of the 148 hospitalizations, all but 49 were due to influenza A, and 67% were in patients ≥65 years of age.

Since the start of the 2014-15 season, 6,249 hospitalizations have been reported; 5,877 (95%) 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 321 ICU admissions have been reported to date: 54% (n=172) were in adults ≥65 years of age and 32% (n=102) were in adults 20-64 years. A total of 462 deaths have been reported since the start of the season: three children <5 years of age, three children 5-19 years, 38 adults 20-64 years, and 418 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 March 26, 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 March 26, 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, 15 new laboratory-confirmed cases of MERS-CoV have been reported by the World Health Organization. Globally, from September 2012 to March 26, 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

Avian Influenza A(H5)
Surveillance by the CFIA has not detected the H5N2 and H5N1 strains of the virus in domestic poultry since February 2, 2015.

• CFIA - Notifiable Avian Influenza

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

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.