FluWatch report: May 3 to May 9, 2015 (Week 18)

Influenza/ILI Activity (geographic spread)

In week 18, one region in BC and one region in NL reported widespread activity. Ten regions reported localized activity: BC(2), ON(6), and QC(2). Twenty-six regions reported sporadic activity: NT, BC, AB(5), SK(3), MB(4), ON, QC(4), NL, NB(5), and NS. Twenty regions reported no activity: YK, NT, NU(3), BC, MB, NL(2), NB(2), NS(8), and PE.

Influenza and Other Respiratory Virus Detections

The number of positive influenza tests decreased from 381 in week 17 to 299 in week 18. Influenza B remained the predominant virus in week 18, representing 89% of influenza detections. Most jurisdictions reported stable or declining levels of influenza detections over recent weeks. To date, 81% 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 36,794 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. Adults under the age of 64 years accounted for 59% of influenza B detections.

In week 18, detections for all other respiratory viruses except rhinovirus and human metapneumovirus decreased from the previous week (figure 3). The percent positive for rhinovirus increased from 13% in week 17 to 20% in week 18.

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

Antiviral Resistance

During the 2014-2015 influenza season, the NML has tested 1,446 influenza viruses for resistance to oseltamivir and 1,444 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 1,365 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 849 influenza viruses [190 A(H3N2), 17 A(H1N1) and 642 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assay (n=190), one virus was antigenically similar to A/Texas/50/2012, five showed reduced titers to A/Texas/50/2012 and 184 were antigenically similar to A/Switzerland/9715293/2013, which is the influenza A(H3N2) component recommended for the 2015 Southern Hemisphere influenza vaccine. Additionally, 1,129 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 1,127 belonged to a genetic group that typically shows reduced titers to A/Texas/50/2012.
Influenza A(H1N1): Seventeen A(H1N1) viruses characterized were antigenically similar to A/California/7/2009.
Influenza B: Of the 642 influenza B viruses characterized, 602 viruses were antigenically similar to B/Massachusetts/2/2012, three viruses showed reduced titers against B/Massachusetts/2/2012, and 37 were B/Brisbane/60/2008-like (Figure 4).

Influenza-like Illness (ILI) Consultation Rate

In week 18, the national influenza-like-illness (ILI) consultation rate increased from the previous week to 23.1 consultations per 1,000 (Figure 5).

Influenza Outbreak Surveillance

In week 18, 14 new outbreaks of influenza were reported: two due to influenza B, one due to influenza A and 11 for which the influenza type was not provided.  Eleven outbreaks were reported in long-term care facilities (LTCF) and three in institutional or community settings (Figure 6). To date this season, 1,265 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

Pharmacy surveillance for sales of influenza antivirals has ended for the 2014-2015 influenza season (Figure 7).

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 18, six laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All 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, three (50%) were <2 years of age and three (50%) were 2 to 9 years of age. One ICU case was reported.

To date this season, 681 hospitalizations have been reported by the IMPACT network, 509 (75%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 98% (161/164) were A(H3N2) (Table 4). To date, 86 cases were admitted to the ICU, of which 49 (57%) were 2 to 9 years of age (Figure 9a). A total of 56 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 (CIRN)

Surveillance has ended for the 2014-2015 influenza season.

This season, 2,228 cases have been reported; 1,912 (86%) with influenza A. The majority of cases (81%) were among adults ≥65 years of age (Table 5). One hundred and seventy two ICU admissions have been reported and 128 cases were adults ≥65 years of age. Among the 172 ICU admissions, 27 were due to influenza B (12 in adults 45 to 64 years of age and 15 in adults over the age of 65). A total of 123 ICU cases (72%) reported to have at least one underlying condition or comorbidity. Of the 123 ICU cases with known immunization status, 40 (33%) reported not having been vaccinated this season. One hundred and thirty-five deaths have been reported, 124 (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 18, 78 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{ootnote *}, which is lower than the number reported the previous week. Of the 78 hospitalizations, 46 (59%) were due to influenza A and 38 (49%) were in patients ≥65 years of age.

Since the start of the 2014-15 season, 7,448 hospitalizations have been reported; 6,510 (87%) with influenza A. Among cases for which the subtype of influenza A was reported, 99.3% were A(H3N2). The majority of cases (70%) were ≥65 years of age (Table 6). A total of 382 ICU admissions have been reported to date: 53% (n=202) were in adults ≥65 years of age and 34% (n=128) were in adults 20-64 years. A total of 562 deaths have been reported since the start of the season: three children <5 years of age, four children 5-19 years, 43 adults 20-64 years, and 512 adults ≥65 years of age. Influenza A has been reported in 92% of deaths. Adults 65 years of age or older represent 91% 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, six new laboratory-confirmed cases of human infection with avian influenza A(H7N9) virus were reported by the World Health Organization. Globally to May 14, 2015, the WHO reported a total of 657 laboratory-confirmed human cases with avian influenza A(H7N9) virus, including 227 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, two new laboratory-confirmed cases of MERS-CoV have been reported by the World Health Organization. Globally, from September 2012 to May 14, 2015, the WHO has reported a total of 1,112 laboratory-confirmed cases of infection with MERS-CoV, including 422 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

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.