FluWatch report: November 22 to November 28, 2015 (week 47)

Overall Summary

  • Based on laboratory detections, influenza activity in week 47 is significantly lower than previous seasons. Other flu indicators support this finding.
  • No new laboratory confirmed outbreaks were reported in week 47.
  • So far this season, influenza A(H3N2) has been the most common subtype affecting Canadians.
  • To date, the majority of influenza laboratory detections and hospitalizations have been in seniors greater than 65 years of age.
  • For more information on the flu, see our Flu(influenza) web page.

Are you a primary health care practitioner (General Practitioner, Nurse Practitioner or Registered Nurse) interested in becoming a FluWatch sentinel for the 2015-16 influenza season? Contact us at FluWatch@phac-aspc.gc.ca

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Influenza/Influenza-like Illness Activity (geographic spread)

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Organization:
Date published: 2015-12-04

In week 47, 17 regions across Canada reported influenza/ILI (up from 12 regions in week 46). The majority of regions across Canada (35) reported no activity in week 47. Overall, low flu activity was reported across the country.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, Week 47

Figure 1
Figure 1 Legend

Note: Influenza/ILI activity levels, as represented on this map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, sentinel ILI rates and reported outbreaks. Please refer to detailed definitions at the end of the report. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.

Figure 1 - Text Description

In week 47, 17 regions across Canada reported influenza/ILI (up from 12 regions in week 46). The majority of regions across Canada (35) reported no activity in week 47. Overall, low flu activity was reported across the country.

Laboratory Confirmed Influenza Detections

The percent positive for influenza detections decreased from 1.47% in week 46 to 1.44% in week 47. Compared to the previous five seasons, the percent positive (1.44%) reported in week 47 was below the five year average for that week and below expected levels (range 2.03% - 8.03%).

Figure 2. Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2015-16

Figure 2
Figure 2 - Text Description

The percent positive for influenza detections decreased from 1.47% in week 46 to 1.44% in week 47.

In week 47, there were 48 laboratory detections of influenza reported (down from 49 detections reported in week 46). BC and QC accounted for the majority  of influenza detections in week 47 (58%). To date, 90% of influenza detections have been influenza A and the majority of those subtyped have been A(H3) (86%).

Figure 3. Cumulative numbers of positive influenza specimens by type/subtype and province, Canada, 2015-16

Figure 3

Note: Specimens from NT, YT, and NU are sent to reference laboratories in other provinces. Cumulative data includes updates to previous weeks.

Figure 3 - Text Description
Reporting
provincesTable Figure 3 - Footnote 1
Weekly (November 22 to November 28, 2015) Cumulative (August 30, 2015 to November 28, 2015)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1)pdm09
A
(H3)
A Table Figure 3 - Footnote UnS B
Total
A
Total
A
(H1)pdm09
A
(H3)
ATable Figure 3 - Footnote UnS B
Total
BC 15 0 14 1 1 171 3 117 51 8 179
AB 3 0 2 1 3 51 4 41 6 13 64
SK 0 0 0 0 0 8 5 0 3 0 8
MB 0 0 0 0 0 1 0 0 1 1 2
ON 6 2 3 1 2 115 21 66 28 14 129
QC 12 1 0 11 1 41 1 0 40 7 48
NB 0 0 0 0 0 0 0 0 0 0 0
NS 0 0 0 0 0 5 0 1 4 0 5
PE 1 1 0 0 0 3 3 0 0 0 3
NL 0 0 0 0 0 2 0 2 0 1 3
YT 0 0 0 0 0 1 0 1 0 0 1
NT 4 0 3 1 0 8 0 7 1 0 8
NU 0 0 0 0 0 0 0 0 0 0 0
Canada 41 4 22 15 7 406 37 235 134 44 450
Percentage Table Figure 3 - Footnote 2 85.4% 9.8% 53.7% 36.6% 14.6% 90.2% 9.1% 57.9% 33.0% 9.8% 100.0%

Among influenza cases with reported age, the largest proportion was in those ≥65 years of age (48%) (Table 1).

Table 1. Weekly and cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reportingTable 1 - Footnote 1, Canada, 2015-16
Age groups (years) Weekly (November 22 to November 28, 2015) Cumulative (August 30, 2015 to November 28, 2015)
Influenza A B Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A Table 1 - Footnote UnS Total A Total A(H1) pdm09 A(H3) A Table 1 - Footnote UnS Total # %
<5 1 0 1 0 1 18 2 13 3 7 25 7.0%
5-19 3 0 1 2 2 24 1 15 8 11 35 9.7%
20-44 8 0 3 5 0 39 3 20 16 6 45 12.5%
45-64 4 1 1 2 0 73 8 48 17 6 79 22.0%
65+ 10 0 1 9 0 165 8 114 43 8 173 48.2%
Unknown 0 0 0 0 0 1 0 1 0 1 2 0.6%
Total 26 1 7 18 3 320 22 211 87 39 359 100.0%
PercentageTable 1 - Footnote 2 89.7% 3.8% 26.9% 69.2% 10.3% 89.1% 6.9% 65.9% 27.2% 10.9%    

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 slightly increased from the previous week. In week 47, the the ILI consultation rate was 23.0 per 1,000 patient visits compared to 21.1 per 1,000 patient visits in week 46. In week 47, the highest ILI consultation rate was found in the 5-19 age group and the lowest was found in the 65+ years of age group (Figure 4).

Figure 4. Influenza-like-illness (ILI) consultation rates by age group and week, Canada, 2015-16

Figure 4

Delays in the reporting of data may cause data to change retrospectively. In BC, AB, and SK, data are compiled by a provincial sentinel surveillance program for reporting to FluWatch. Not all sentinel physicians report every week.

Figure 4 - Text Description

Influenza-like illness consultation rate by age-group in week 45 for the 2015-16 season:
Age 0-4: 49.57; Age 5-19: 68.42; Age 20-64: 10.91; Age 65+: 4.75

Influenza Outbreak Surveillance

In week 47, one outbreak of ILI was reported in a school.  To date this season, 15 outbreaks have been reported (ten of which occurred in LTCFs). Last year at this time, 37 outbreaks were reported (35 of which occurred in LTCFs).

Figure 5. Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2015-2016

Figure 5
Figure 5 - Text Description
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 0 0
37 1 1 0
38 0 0 0
39 0 2 0
40 0 2 1
41 0 0 0
42 0 0 0
43 0 1 0
44 1 3 1
45 1 1 0
46 0 0 0
47 0 0 0

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

To date this season, twelve 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, two cases were due to influenza B. 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.

Figure 6. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group, Canada, 2015-16, Paediatric hospitalizations (≤16 years of age, IMPACT)

Figure 6
Figure 6 - Text Description

Data supressed for the 2015-16 season due to small values. Figure  6 will be updated  when additional data are received.

Figure 7. Number of cases of influenza reported by sentinel hospital networks, by week, Canada, 2015-16 paediatric hospitalizations (≤16 years of age, IMPACT)

Figure 7

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.

Figure 7 - Text Description
Report week Influenza A Influenza B Co-infection A & B
35 0 0 0
36 0 0 0
37 1 0 0
38 2 0 0
39 0 0 0
40 0 0 0
41 1 0 0
42 0 0 0
43 0 1 1
44 0 0 1
45 1 1 0
46 1 0 0
47 2 0 0

Provincial/Territorial Influenza Hospitalizations and Deaths

Since the start of the 2015-16 season, 70 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territoriesFootnote *; all but eight with influenza A. Among cases for which the subtype of influenza A was reported, 75% (27/36) were A(H3). The majority (56%) 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 47, a total of 145 hospitalizations were reported by participating provinces and territories.

Figure 8. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group, Canada 2015-16

Figure 8
Figure 8 - Text Description
Age-group (years) Hospitalizations (n=70) ICU admissions (n=5) Deaths (n=3)
0-4 7.1% 0.0% 0.0%
5-19 2.9% 0.0% 0.0%
20-44 10.0% 40.0% 33.3%
45-64 24.3% 40.0% 0.0%
65+ 55.7% 20.0% 66.7%

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 45 influenza viruses [34 A(H3N2), 2 A(H1N1) and 9 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 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 33 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): Two 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 48 influenza viruses for resistance to oseltamivir and zanamivir. All viruses were sensitive to zanamivir and oseltamivir. A total of 39 influenza A viruses tested for amantadine, all but one were resistant (98%). (Table 2).

Table 2. Antiviral resistance by influenza virus type and subtype, Canada, 2015-16
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 37 0 37 0 39 38 (97.4%)
A (H1N1) 2 0 2 0 1 1 (100%)
B 9 0 9 0 NA Table 2 - Footnote * NA Table 2 - Footnote *
TOTAL 48 0 48 0 40 39

International Influenza Reports


FluWatch definitions for the 2015-2016 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 ILIFootnote * 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 regionFootnote

4 = Widespread:

  1. evidence of increased ILIFootnote * 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 regionFootnote

Note: ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls.

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