FluWatch report: January 18 to January 24, 2015 (Week 3)

Influenza/ILI Activity (geographic spread)

In week 03, 15 regions reported widespread activity: in BC(2), ON(5), QC(4), NF(3) and PEI. Twenty-five regions reported localized activity: in BC(3), AB(5), MB(5), ON(2), QC(2), NB(6), NS(6) and NL and seven regions reported sporadic activity: in NWT, YK, SK(3), NB and NF. NU did not report data for week 03.

Influenza and Other Respiratory Virus Detections

The number of positive tests decreased from 3,829 in week 02 to 2,928 in week 03. The percentage of positive influenza tests also decreased slightly from 28.3% to 27.4% (Figure 2). To date, 97% of influenza detections have been influenza A, and 99.8% of those subtyped have been A(H3N2) (Table 1).To date this season, detailed information on age and type/subtype has been received for 24,071 cases. A significantly greater proportion of laboratory detections of influenza have been reported in adults ≥65 years of age (63%) this season compared to the 2013-14 season when only 15.4% of cases were in adults ≥65 years of age (Table 2).

In week 03, the number of positive respiratory syncytial virus (RSV) tests decreased to 894 RSV detections and remains the second most frequently detected virus after influenza. Detections of RSV since week 38 have been higher than in the previous season. Detections of other respiratory viruses have been declining and have generally been lower this season compared to the previous season (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 317 influenza viruses for resistance to oseltamivir and 313 influenza viruses for resistance to zanamivir and all were sensitive to both agents. A total of 605 (99.8%) of 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 132 influenza viruses [68 A(H3N2), 2 A(H1N1) and 62 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=68), one virus was antigenically similar to A/Texas/50/2012, five showed reduced titers to A/Texas/50/2012 and 62 were antigenically similar to A/Switzerland/9715293/2013, which is the influenza A(H3N2) component recommended for the 2015 Southern Hemisphere influenza vaccine. Additionally, 474 A(H3N2) viruses were unable to be tested by HI assay; however, sequence analysis showed that 472 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 62 influenza B viruses characterized, 56 viruses were antigenically similar to B/Massachusetts/2/2012, three viruses showed reduced titers against B/Massachusetts/2/2012, and three were B/Brisbane/60/2008-like (Figure 4).

Influenza-like Illness (ILI) Consultation Rate

The national influenza-like-illness (ILI) consultation increased in week 03 to 45.3 consultations per 1,000, which is slightly above expected levels (Figure 5).

Influenza Outbreak Surveillance

In week 03, 72 new outbreaks of influenza were reported, nearly half the number of outbreaks reported in the previous week. Fifty-four outbreaks were reported in long-term care facilities (LTCF), six in hospitals and 12 in institutional or community settings (Figure 6). Among the outbreaks in which the influenza subtype was known, seven LTCF outbreaks and one institutional or community setting outbreak were associated with A(H3N2), and four LTCF outbreaks associated with influenza B. To date this season, 795 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 03, the proportion of prescriptions for antivirals decreased to 511.3 antiviral prescriptions per 100,000 total prescriptions (down from 806.1 per 100,000). The rate for antivirals since week 48 has been higher than the previous three seasons (Figure 7). The rate in age groups except in infants decreased in week 03. The antiviral prescription rate remains the highest amongst seniors at 859.9 per 100,000 total prescriptions.

Sentinel Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

In week 03, 29 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network: 28 cases of influenza A and one case of influenza B (Figure 8a). Among the reported cases, 12 (41%) were <2 years of age, 15 (52%) were 2 to 9 years of age and two (7%) were 10-16 years of age. Three cases were admitted to the ICU. To date this season, 446 hospitalizations have been reported by the IMPACT network, 421 (94%) of which were cases of influenza A. Among cases for which the influenza A subtype was reported, 99% (137/139) were A(H3N2)  (Table 4). To date, 50 cases were admitted to the ICU, of which 32 (64%) were 2 to 9 years of age (Figure 9a). Two 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 03, 98 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 cases in week 03, 81 cases (83%) were in adults over the age of 65 and 94 cases (96%) had influenza A (Figure 8b). To date this season, 1259 cases have been reported; 1244 (99%) with influenza A. The majority of cases (84%) were among adults ≥65 years of age (Table 5). Eighty-eight ICU admissions have been reported and the majority of cases (80%) were adults ≥65 years of age, most (83%) with known underlying conditions or comorbidities. Fifty-four 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 03, 357 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *} ; all but one with influenza A, and 74% were patients ≥65 years of age. Since the start of the 2014-15 season, 3,589 hospitalizations have been reported; 3,523 (98%) with influenza A. Among cases for which the subtype of influenza A was reported, 99.7% (1720/1725) were A(H3N2). The majority of cases (71%) were ≥65 years of age (Table 6). A total of 104 ICU admissions have been reported in adults ≥65 years of age with influenza A and 52 ICU admissions have been reported in adults 20-64 years. A total of 236 deaths have been reported since the start of the season:  one child <5 years of age, two children 5-19 years, sixteen adults 20-64 years, and 217 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): On January 26, 2015, the first imported human case of avian influenza A (H7N9) from China was confirmed in Canada. A second case was confirmed on January 29, 2015. They traveled together to China and recently returned to Canada. All evidence regarding the Canadian cases indicates they were likely infected following exposure in China. They were not symptomatic during travel and only became ill after arrival in Canada. These are the first documented cases of H7N9 infection in humans in North America. The risk to Canadians of getting sick with H7N9 remains very low as evidence suggests that it does not transmit easily from person-to-person.

Since the last FluWatch report, one new laboratory-confirmed case of human infection with avian influenza A(H7N9) virus was reported by the World Health Organization (not including the Canadian cases). The case was a 79 year-old male with a history of exposure to live poultry. The case has been in stable condition all along. Globally to January 30, 2015, the WHO reported a total of 486 laboratory-confirmed human cases with avian influenza A(H7N9) virus, including 185 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, 6 new laboratory-confirmed cases of MERS-CoV have been reported by the World Health Organization from Saudi Arabia (5) and Oman (1). Globally, from September 2012 to January 30, 2015, the WHO has been informed of a total of 956 laboratory-confirmed cases of infection with MERS-CoV, including 351 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. No new sites have been identified since December 19, 2014. Further information on the outbreak is provided on the following CFIA website.

• CFIA - Notifiable Avian Influenza

Enterovirus D68 (EV-D68)

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.

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.