FluWatch report: December 13 to December 19, 2015 (week 50)

Overall Summary

  • In week 50, several influenza surveillance indicators revealed that influenza activity is on the rise nationally compared to previous weeks.
  • Laboratory detections of influenza are below expected levels for this time of the year.
  • So far this season, influenza A(H3N2) has been the most common subtype affecting Canadians. An increase in the number of influenza A(H1N1) cases has been noted over the past few  weeks.  
  • 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.

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Organization: Public Health Agency of Canada

Date published: 2015-12-30

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 50, 20 regions across Canada reported influenza/ILI. Overall, low flu activity was reported across the country, however a slight increase in activity levels was reported compared to week 49. Localized activity was reported in two regions of Ontario.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, Week 50

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 50, 20 regions across Canada reported influenza/ILI. Overall, low flu activity was reported across the country; however a slight increase in activity levels was reported compared to week 49. Localized activity was reported in two regions of Ontario.

Laboratory Confirmed Influenza Detections

The percent positive for influenza detections increased from 1.64% in week 49 to 2.42% in week 50. Compared to the previous five seasons, the percent positive (2.42%) reported in week 50 was below the five year average for that week and below expected levels (range 7.81%-23.75%).

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 increased from 1.64% in week 49 to 2.42% in week 50.

In week 50, there were 93 laboratory detections of influenza reported (up from 48 detections reported in week 49). To date, 89% of influenza detections have been influenza A and the majority of those subtyped have been A(H3) [(78% (283/363)]. Please note Figure 3 depicts data as of week 49.

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 (December 6 to December 12, 2015) Cumulative (August 30, 2015 to December 12, 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 11 0 6 5 2 186 3 123 60 11 197
AB 8 0 4 4 2 65 6 50 9 15 80
SK 0 0 0 0 1 10 5 1 4 1 11
MB 0 0 0 0 0 1 0 0 1 1 2
ON 19 8 6 5 1 142 33 74 35 16 158
QC 7 1 0 6 2 53 2 0 51 10 63
NB 0 0 0 0 0 0 0 0 0 0 0
NS 1 0 0 1 0 6 0 1 5 0 6
PE 1 1 0 0 0 4 4 0 0 0 4
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 2 0 2 0 0 16 0 16 0 0 16
NU 0 0 0 0 0 0 0 0 0 0 0
Canada 49 10 18 21 8 486 53 268 165 55 541
Percentage Table Figure 3 - Footnote 2 86.0% 20.4% 36.7% 42.9% 14.0% 89.8% 10.9% 55.1% 34.0% 10.2% 100.0%

Among influenza cases with reported age, the largest proportion was in those ≥65 years of age (42%) (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 (December 13 to December 19, 2015) Cumulative (August 30, 2015 to December 19, 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 5 1 1 3 0 33 5 18 10 9 42 8.5%
5-19 7 0 2 5 3 37 5 21 11 21 58 11.7%
20-44 9 2 3 4 1 65 12 34 19 10 75 15.2%
45-64 9 1 2 6 1 100 19 55 26 11 111 22.4%
65+ 10 2 0 8 3 195 9 128 58 11 206 41.6%
Unknown 0 0 0 0 0 2 1 1 0 1 3 0.6%
Total 40 6 8 26 8 432 51 257 124 63 495 100.0%
PercentageTable 1 - Footnote 2 83.3% 15.0% 20.0% 65.0% 16.7% 87.3% 11.8% 59.5% 28.7% 12.7%    

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 increased from the previous week. In week 50, the ILI consultation rate was 23.2 per 1,000 patient visits compared to 21.0 per 1,000 patient visits in week 49. In week 50, the highest ILI consultation rate (37.2 per 1,000) visits was found in those 5-19 years of age and the lowest was found in the >65 yrs 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 50 for the 2015-16 season:
Age 0-4: 42.44; Age 5-19: 29.35; Age 20-64: 24.02; Age 65+: 0.11

Influenza Outbreak Surveillance

In week 50, one new laboratory confirmed outbreak was reported. The outbreak was reported in a Long Term Care Facility (LTCF). To date this season, 27 outbreaks have been reported (13 of which occurred in LTCFs). Last year at this time, 183 outbreaks were reported (141 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
48 0 1 0
49 0 1 0
50 0 1 0

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

To date this season, 18 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the Immunization Monitoring Program Active (IMPACT) network. Fifteen hospitalized cases were due to influenza A and three cases were due to influenza B. Additionally, not included in Table 2 and Figure 6, 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.

Table 2- Cumulative numbers of paediatric hospitalizations with influenza reported by the IMPACT network, Canada, 2015-16
Age Groups Cumulative (30 Aug. 2015 to 19 Dec. 2015) 
Influenza A Influenza B
A Total A(H1) pdm09 A(H3) A (UnS) B Total
0-5m <5 0 <5 <5 0
6-23m <5 0 <5 <5 0
2-4y <5 0 0 <5 <5
5-9y <5 0 0 <5 <5
10-16y <5 0 0 <5 0

Figure 6. Number of cases of influenza reported by sentinel hospital networks, by week, Canada, 2015-16, paediatric and adult hospitalizations (≤16 years of age, IMPACT; ≥16 years of age, CIRN-SOS)

Figure 6

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 6 - Text Description
Report week Influenza A Influenza B
35 0 0
36 0 0
37 1 0
38 2 0
39 0 0
40 0 0
41 1 0
42 0 0
43 1 0
44 0 0
45 2 0
46 1 2
47 2 0
48 2 1
49 3 4
50 3 0

Adult Influenza Hospitalizations and Deaths

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

Table 3 - Cumulative numbers of adult hospitalizations (≥16 years of age) with influenza reported by the CIRN-SOS network, Canada, 2015-16
Age groups (years) Cumulative (1 Nov. 2015 to 19 Dec. 2015)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A(UnS) Total # (%)
16-20 0 0 0 0 0 0 (%)
20-44 1 0 0 1 0 1 (10%)
45-64 2 0 1 1 1 3 (30%)
65+ 6 0 4 2 0 6 (60%)
Total 9 0 5 4 1 10
% 90% 0% 56% 44% 10% 100%

Figure 7. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥16 year of age), Canada 2015-16

Figure 7
Figure 7 - Text Description
Age-group (years) Hospitalizations (n=10) ICU admissions (n=0) Deaths (n=0)
16-20 0.0% 0.0% 0.0%
20-44 10.0% 0.0% 0.0%
45-64 30.0% 0.0% 0.0%
65+ 60.0% 0.0% 0.0%

Provincial/Territorial Influenza Hospitalizations and Deaths

Since the start of the 2015-16 season, 105 laboratory-confirmed influenza-associated hospitalizations were reported from participating provinces and territoriesFootnote *; all but nine with influenza A. Among cases for which the subtype of influenza A was reported, 73% (37/51) were A(H3). The majority (49%) of patients were ≥65 years of age. Eight ICU admissions and three deaths have been reported. All reported ICU admissions and deaths were in adults. Last year, in week 50, a total of 492 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=105) ICU admissions (n=8) Deaths (n=3)
0-4 10.5% 0.0% 0.0%
5-19 4.8% 0.0% 0.0%
20-44 11.4% 25.0% 33.3%
45-64 24.8% 37.5% 0.0%
65+ 48.6% 37.5% 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 119 influenza viruses [71 A(H3N2), 24 A(H1N1) and 24 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays,six 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 65 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): Twenty-four H1N1 virus characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B: Sixteen influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013. Eight 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 115 influenza viruses for resistance to oseltamivir and zanamivir and 91 influenza viruses for resistance to amantadine. All viruses were sensitive to zanamivir and oseltamivir. A total of 90 influenza A viruses (99%) were resistant to amantadine. (Table 4).

Table 4. 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) 70 0 70 0 75 74 (98.7%)
A (H1N1) 22 0 22 0 16 16 (100%)
B 23 0 23 0 NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 115 0 115 0 91 90

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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