FluWatch report: October 18 to October 24, 2015 (week 42)

Laboratory Confirmed Influenza Detections

In week 42, the percent positive for influenza detections remained low at 0.85%. The percent positive reported this week is lower than the percent positive reported the same week last season (1.96%). Since week 39, the percent positive for influenza detections have been decreasing (Figure 2).

In week 42, the majority of detections in Canada have been reported from BC and ON, accounting for 75% of the influenza detections in Canada. A total of six jurisdictions have not reported any influenza cases. To date, 92% of influenza detections have been influenza A and the majority of those subtyped have been A(H3).

Among cases with reported age, the largest proportion was in those ≥65 years of age (48%) (Table 1). Compared to the previous year during the same period, a greater proportion of cases in the 20-44 and 45-64 age groups have been reported to date (40% this year vs 24% last year)

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 influenza-like-illness (ILI) consultation rate increased from 22.3 consultations per 1,000 patient visits in week 41 to 31.4 per 1,000 visits in week 42. In week 42, the highest ILI consultation rate was found in the 0-4 age group and the lowest was found in the ≥65 years of age group (Figure 4).

Influenza Outbreak Surveillance

In week 42, no new laboratory-confirmed outbreaks of influenza were reported (Figure 5). There was one outbreak of ILI reported in a school. To date this season, seven outbreaks have been reported, which is lower than the number of outbreaks reported last year at this time (n=11).

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths (IMPACT)

To date this season, less than five laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the Immunization Monitoring Program Active (IMPACT) network. All hospitalized cases were due to influenza A. To date, less than five ICU admissions have been reported.

Provincial/Territorial Influenza Hospitalizations and Deaths

Since the start of the 2015-16 season, 37 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territories^{Footnote *}. All but three hospitlaizations were due to influenza A. The majority (60%) of patients were ≥65 years of age. Four ICU admissions have been reported.

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 12 influenza viruses [8 A(H3N2), 1 A(H1N1) and 3 influenza B].

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

Sequence analysis was done on seven H3N2 viruses. All seven 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 Northern Hemisphere's vaccine.

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

Influenza B: The three influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013.

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 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 (HAI) testing compared to the reference influenza strains recommended by WHO.

Antiviral Resistance

During the 2015-16 season, the National Microbiology Laboratory (NML) has tested 17 influenza viruses for resistance to oseltamivir and zanamivir. All viruses were sensitive to zanamivir and oseltamivir. All influenza A viruses tested were resistant to amantadine (Table 2).

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.