FluWatch report: January 3, 2016 – January 9, 2016 (week 1)

Influenza/Influenza-like Illness Activity (geographic spread)

In week 01, 25 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in four regions in Canada (two in ON, one each in AB and NL).

Laboratory Confirmed Influenza Detections

Laboratory confirmed influenza detections continue to increase steadily. The percent positive for influenza increased from 4.3% in week 52 to 6.0% in week 01 (Figure 2). Compared to the previous five seasons, the percent positive (6.0%) reported in week 01 was below the five year average for that week and below expected levels (range 14.3%-33.2%).

In week 01, there were 306 positive influenza tests reported. Similar to the previous two weeks, the majority of subtyped influenza A viruses detected in Canada were influenza A(H1N1). Influenza A(H1N1) was the most common influenza A subtype detected in AB, SK, ON, NB, and PE in week 01. To date, 83% of influenza detections have been influenza A and among those subtyped approximately half have been influenza A(H3N2) [52% (344/659)].

To date this season, detailed information on age and type/subtype has been received for 864 cases. Adults aged 65 years and older accounted for 35% of reported influenza cases (Table 1). Adults aged 65 years and older also represented 47% of reported A(H3N2) cases. Adults aged 20-44 years represented 27% of reported influenza A(H1N1) cases and 24% of reported influenza B cases.

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 from 41.5 per 1,000 patient visits in week 52, to 28.4 per 1,000 patient visits in week 01. In week 01, the highest ILI consultation rate was found in those 0-4 years (62.5 per 1,000) of age and the lowest was found in the ≥65 years age group (Figure 4).

Influenza Outbreak Surveillance

In week 01, three new laboratory confirmed influenza outbreaks were reported. Two outbreaks were reported in long-term care facilities (LTCF) and one was due to influenza A. The other outbreak was reported in a institutional or community setting. To date this season, 36 outbreaks have been reported (17 of which occurred in LTCFs). In comparison, at week 01 in the 2014-15 season, 601 outbreaks were reported (471 of which occurred in LTCFs) and in the 2013-14 season, 34 outbreaks were reported (28 of which occurred in LTCFs).

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 01, sixteen hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network (Figure 6). Eight hospitalizations were due to influenza A(H1N1) (50%).

To date this season, 54 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the IMPACT network. Forty-three hospitalized cases were due to influenza A and eleven cases were due to influenza B. The majority of hospitalized cases were among children aged 2-4 years (53%). Additionally, not included in Table 2 and Figure 6, two cases were due to co-infections of influenza A and B. To date, seven intensive care unit (ICU) admissions and less than five influenza-associated 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

In week 01, sixteen hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS),up from eight hospitalizations reported in week 52 (Figure 6). The majority of hospitalizations were in adults ≥65 years of age (63%) and due to influenza A (63%).

To date this season, 41 laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations have been reported by CIRN-SOS. The majority of hospitalized cases were due to influenza A (78%) and were among adults ≥65 years of age (54%). One intensive care unit (ICU) admission has been reported. No 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.

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 01, 40 hospitalizations have been reported from participating provinces and territories^{Footnote *}. The majority of hospitalizations were in adults ≥65 years of age (30%); however, the 0-4 age group and 45-64 age group followed closely representing 28% and 25% of hospitalizations respectively. Influenza A(H1N1) accounted for 60% of hospitalizations and among influenza A(H1N1) hospitalizations, nine (38%) were among children aged 0-4.

Since the start of the 2015-16 season, 201 laboratory-confirmed influenza-associated hospitalizations have been reported. One hundred and seventy-six hospitalizations (88%) were due to influenza A and twenty-five (12%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 53% (40/96) were influenza A(H1N1). The majority (43%) of hospitalized cases were ≥65 years of age. Eighteen ICU admissions and ten deaths 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 156 influenza viruses [86 A(H3N2), 39 A(H1N1) and 31 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, eight 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 78 H3N2 viruses. All 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): Thirty-nine H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B: Twenty influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. Eleven influenza B viruses were 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 152 influenza viruses for resistance to oseltamivir and 151 influenza viruses for zanamivir. All viruses were sensitive to zanamivir and oseltamivir. A total of 113 influenza A viruses (99%) 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:

• evidence of increased ILI^{Footnote *} and

1. lab confirmed influenza detection(s) together with
2. 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.