FluWatch report: November 29 to December 5, 2015 (week 48)

In week 48, 15 regions across Canada reported influenza/ILI (down from 17 regions in week 47). The majority of regions across Canada (38) reported no activity in week 48. Overall, very low flu activity was reported across the country.

Laboratory Confirmed Influenza Detections

The percent positive for influenza detections decreased from 1.44% in week 47 to 0.85% in week 48. Compared to the previous five seasons, the percent positive (0.85%) reported in week 48 was below the five year average for that week and below expected levels (range 3.17% - 12.11%).

In week 48, there were 27 laboratory detections of influenza reported (down from 48 detections reported in week 47). To date, 90% of influenza detections have been influenza A and the majority of those subtyped have been A(H3) (86%).

Among influenza cases with reported age, the largest proportion was in those ≥65 years of age (50%) (Table 1).

For additional data on other respiratory virus detections see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada website.

Influenza-like Illness Consultation Rate

The national ILI consultation rate decreased from the previous week. In week 48, the ILI consultation rate was 16.7 per 1,000 patient visits compared to 23.0 per 1,000 patient visits in week 47. In week 48, the highest ILI consultation rate was found in the 20-64 age group and the lowest was found in the 65+ years of age group (Figure 4).

Influenza Outbreak Surveillance

In week 48, no new outbreaks were reported.  To date this season, 15 outbreaks have been reported (ten of which occurred in LTCFs). Last year at this time, 58 outbreaks were reported (52 of which occurred in LTCFs).

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

To date this season, eleven laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the Immunization Monitoring Program Active (IMPACT) network. Eight hospitalized cases were due to influenza A, three cases was due to influenza B. Additionally, not shown in the table, a total of  two cases were due to co-infections of influenza A and B. To date, less than five intensive care unit (ICU) admissions 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

To date this season, three laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations have been reported by the Canadian Immunization Research Network Serious Outcome Sutveillance (CIRN-SOS). All hospitalized cases were due to influenza A. To date, no intensive care unit (ICU) admissions or deaths have been reported.

Provincial/Territorial Influenza Hospitalizations and Deaths

Since the start of the 2015-16 season, 79 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *}; all but eight with influenza A. Among cases for which the subtype of influenza A was reported, 74% (29/39) were A(H3). The majority (54%) of patients were ≥65 years of age. Five ICU admissions and three deaths have been reported.All reported ICU admissions and deaths were in adults. Last year, in week 48, a total of 224 hospitalizations were reported by participating provinces and territories.

See additional data on Reported Influenza Hospitalizations and Deaths in Canada: 2011-12 to 2015-16 on the Public Health Agency of Canada website.

Influenza Strain Characterizations

During the 2015-16 influenza season, the National Microbiology Laboratory (NML) has characterized 54 influenza viruses [40 A(H3N2), 5 A(H1N1) and 9 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, three H3N2 virus  were antigenically characterized as A/Switzerland/9715293/2013-like using antiserum raised against cell-propagated A/Switzerland/9715293/2013.

Sequence analysis was done on 37 H3N2 viruses. All 33 viruses belonged to a genetic group for which most viruses were antigenically related to A/Switzerland/9715293/2013.

A/Switzerland/9715293/2013 is the A(H3N2) component of the 2015-16 Northern Hemisphere's vaccine.

Influenza A (H1N1): Five H1N1 virus characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B: Seven influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013. Two influenza B virus was characterized as B/Brisbane/60/2008-like, one of the influenza B components of the 2015-16 Northern Hemisphere quadrivalent influenza vaccine.

The recommended components for the 2015-2016 northern hemisphere trivalent influenza vaccine include: an A/California/7/2009(H1N1)pdm09-like virus, an /Switzerland/9715293/2013(H3N2)-like virus, and a B/Phuket/3073/2013 -like virus (Yamagata lineage). For quadrivalent vaccines, the addition of a B/Brisbane/60/2008-like virus (Victoria lineage) is recommended.

The NML receives a proportion of the number of influenza positive specimens from provincial laboratories for strain characterization and antiviral resistance testing. Characterization data reflect the results of haemagglutination inhibition testing compared to the reference influenza strains recommended by WHO.

Antiviral Resistance

During the 2015-16 season, the National Microbiology Laboratory (NML) has tested 61 influenza viruses for resistance to oseltamivir and zanamivir. All viruses were sensitive to zanamivir and oseltamivir. All but two influenza A viruses tested (n=52) were resistant to amantadine (Table 4).

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 2015-2016 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.