FluWatch report: January 4 to January 10, 2015 (Week 1)

Influenza/ILI Activity (geographic spread)

In week 01, 22 regions reported widespread activity: in BC(3), AB(5), SK, MB(2), ON(5), QC(3), NF(3). The same five regions in Alberta have reported widespread activity for the past 3 weeks. Thirteen regions reported localized activity: in SK, MB(3), ON, QC(3), NB(4) and PE and eight regions reported sporadic activity: in BC(2), SK, ON, NB(2), NF and NWT.

Influenza and Other Respiratory Virus Detections

The number of positive tests decreased from 5,313 in week 53 to 4,579 in week 01. The percentage of positive influenza tests also decreased from 34.4% to 28.5% (Figure 2). This may be an indication that we have reached the peak in laboratory detections with the percent positive for influenza peaking in week 52 (35%) and the number of positive influenza tests peaking in week 53 (5,313). To date, 98% of influenza detections have been influenza A, and 99.8% 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 (63%) (Table 2).

In week 01, the number of positive RSV tests increased to 1,001 RSV detections up from 979 RSV detections in week 53. RSV remains the second most frequently detected virus after influenza. Detections of RSV since week 38 have been higher than in the previous season while detections of parainfluenza and adenovirus continue to follow their seasonal patterns of broad winter circulation (figure 3).

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

Antiviral Resistance

During the 2014-2015 influenza season, NML has tested 235 influenza viruses for resistance to oseltamivir and 233influenza viruses for resistance to zanamivir and all were sensitive to both agents. A total of 339 (99.7%) of influenza A viruses tested for amantadine resistance were resistant (Table 3).

Influenza Strain Characterizations

During the 2014-2015 influenza season, the National Microbiology Laboratory (NML) has characterized 89 influenza viruses [55 A(H3N2), 2 A(H1N1) and 32 influenza B]. The majority of circulating influenza B and A(H1N1) viruses have been antigenically similar (good match) to the recommended strains for the 2014-15 seasonal influenza vaccine, while the majority of A(H3N2) viruses have shown evidence of an antigenic drift (sub-optimal match) from the vaccine strain.

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assay (n=55), one virus was antigenically similar to A/Texas/50/2012, five showed reduced titers to A/Texas/50/2012 and 49 were antigenically similar to A/Switzerland/9715293/2013, which is the influenza A(H3N2) component recommended for the 2015 Southern Hemisphere influenza vaccine. Additionally, 250 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 249 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 32 influenza B viruses characterized, 29 viruses were antigenically similar to B/Massachusetts/2/2012, and three viruses showed reduced titers (Figure 4).

Influenza-like Illness (ILI) Consultation Rate

The national influenza-like-illness (ILI) consultation decreased in week 01 to 50.1 consultations per 1,000, which is above expected levels for week 01 (Figure 5). The rates were highest among the 0 to 4 years of age group (269.8 consultations per 1,000) and lowest among the adults ≥65 years of age (12.0 consultations per 1,000).

Influenza Outbreak Surveillance

In week 01, 195 new outbreaks of influenza were reported: 152 in long-term care facilities (LTCF), 12 in hospitals and 31 in institutional or community settings  (Figure 6). Among the outbreaks in which the influenza subtype was known, two LTCF outbreaks and four institutional or community setting outbreaks were associated with A(H3N2). To date this season, 623 outbreaks in LTCFs have been reported. The number of outbreaks reported since week 47 is above those of previous seasons and is similar to the numbers reported during the 2012-13 influenza season when influenza A(H3N2) also predominated. The majority of the outbreaks with known subtypes are attributable to A(H3N2).

Pharmacy surveillance

During week 01, the proportion of prescriptions for antivirals decreased to 918.5 antiviral prescriptions per 100,000 total prescriptions (down from 969.6 per 100,000 total prescriptions). The rate for antivirals since week 48 has been higher than the previous three seasons (Figure 7). The rate in age groups except children decreased in week 01. The antiviral prescription rate remains the highest amongst seniors at 1,552.8 per 100,000 total prescriptions.

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 01, 44 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network: 41 cases of influenza A and one case of influenza B (Figure 8a). Among the reported cases, 21 (48%) were <2 years of age, 19 (43%) were 2 to 9 years of age and 4 (9%) were 10-16 years of age. Four cases were admitted to the ICU. To date this season, 358 hospitalizations have been reported by the IMPACT network, 337 (94%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 98% (127/129) were A(H3N2). Children <5 years of age represented 61% of cases  (Table 4). To date, 38 cases were admitted to the ICU, of which 22 (58%) 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 01, 106 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, compared to 137 in week 53. Among cases in week 01, 96 cases (91%) were in adults over the age of 65 and 105 cases (99%) had influenza A (Figure 8b). To date this season, 672 cases have been reported; 664 (99%) with influenza A. The majority of cases (85%) were among adults ≥65 years of age (Table 5). Forty ICU admissions have been reported and the majority of cases (75%) were adults ≥65 years of age, most (69%) with known underlying conditions or comorbidities. Twenty-six deaths have been reported, all but three 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 01, 566 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *} ; all but eight with influenza A, and 79% were patients ≥65 years of age. Since the start of the 2014-15 season, 2161 hospitalizations have been reported; 2121 (98%) with influenza A. Among cases for which the subtype of influenza A was reported, 99.6% (914/917) were A(H3N2). The majority of cases (69%) were ≥65 years of age (Table 6). Sixty two ICU admissions have been reported in adults ≥65 years of age with influenza A and 34 ICU admissions have been reported in adults 20-64 years. A total of 125 deaths have been reported since the start of the season: one child <5 years of age, one child 5-19 years, six adults 20-64 years, and 117 adults ≥65 years of age. Adults 65 years of age or older represent 94% 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 case of human infection with avian influenza A(H7N9) virus have been reported by the World Health Organization. Globally to January 16, 2015, the WHO has been informed of a total of 470 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)

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 January 16, 2015, the WHO has been informed of a total of two cases of avian influenza A (H5N6) virus, including one death.

Middle East Respiratory Syndrome Coronavirus (MERS-CoV)
Since the last FluWatch report, 5 new laboratory-confirmed cases of MERS-CoV have been reported by the World Health Organization. Globally, from September 2012 to January 16, 2015, the WHO has been informed of a total of 950 laboratory-confirmed cases of infection with MERS-CoV, including 350 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 11 commercial infected premises and one non-commercial infected premise. No new sites have been identified since December 19, 2014. Strict surveillance will continue in the area for the next 90 days and if no additional cases of avian influenza are found within this period, the zone can be considered free of avian influenza. 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 website.

• CFIA - Notifiable Avian Influenza

Enterovirus D68 (EV-D68)
BCCDC reported a death associated with EV-D68 in a young child <5 years of age which occurred earlier in the fall of 2014. Additional information is provided in the following report:

• British Columbia Influenza Surveillance BulletinInfluenza Season 2014-15, Number 11, Weeks 51-52 December 14 to 27, 2014

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

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.