FluWatch report: February 21, 2016 - February 27, 2016 (week 08)

Overall Summary

  • Overall in week 08, influenza activity  continued to increase; the  Eastern provinces of Canada accounted for the majority of influenza laboratory confirmations.
  • In week 08, adults 65+ years of age accounted for the largest proportion of hospitalizations
  • The number of outbreaks reported in week 08 increased sharply from the previous week with the majority of outbreaks reported in long-term care facilities. 
  • Influenza A(H1N1) remains the most common influenza subtype circulating in Canada.
  • For more information on the flu, see our Flu(influenza) web page.

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Organization: Public Health Agency of Canada

Date published: 2016-03-04

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 08, a larger proportion of regions reported elevated activity levels in the Eastern regions of Canada. A total of 20 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 20 regions in Canada and widespread activity was reported in one region of PE.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, week 08

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 08, a larger proportion of regions reported elevated activity levels in the central and eastern regions of Canada. A total of 20 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 20 regions in Canada and widespread activity was reported in one region of PE.

Laboratory Confirmed Influenza Detections

Laboratory confirmed influenza detections continued to increase. The percent positive for influenza increased from 29% in week 07 to 33% in week 08 (Figure 2). Compared to the previous five seasons, the percent positive (33%) reported in week 08 was above the five year average for that week and exceeded the expected levels (range 13.0%-17.4%). With the late start to the 2015-16 influenza season, these above normal levels are not unexpected and are typical of peak season levels.

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 increased from 29% in week 07 to 33% in week 08.

In week 08, there were 3,411 positive influenza tests reported. Influenza A(H1N1) continues to be the most common subtype detected. Increased detections of influenza in the central and eastern provinces have been noted in the last few weeks. In week 08, the majority of influenza detections were reported in the provinces of ON and QC (69%). To date, 87% of influenza detections have been influenza A and among those subtyped, the majority have been influenza A(H1N1) [85% (5272/6204)].

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 (February 21 to February 27, 2016) Cumulative (August 30, 2015 to February 27, 2016)
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 124 74 9 41 77 979 349 295 335 791 1770
AB 419 322 6 100 108 2592 2318 130 144 493 3085
SK 163 121 2 40 18 931 620 17 294 111 1042
MB 83 9 <5 Table Figure 3 - Footnote x <5 196 65 32 99 12 208
ON 927 420 35 472 133 2741 1429 252 1060 400 3141
QC 1,125 137 0 988 100 2703 346 3 2354 220 2923
NB 54 6 <5 Table Figure 3 - Footnote x <5 153 27 <5 Table Figure 3 - Footnote x 6 159
NS 16 0 0 16 <5 Table Figure 3 - Footnote x Table Figure 3 - Footnote x <5 56 <5 Table Figure 3 - Footnote x
PE <5 <5 0 0 0 36 36 0 0 0 36
NL 32 0 0 32 <5 80 29 <5 Table Figure 3 - Footnote x <5 Table Figure 3 - Footnote x
YT 7 6 Table Figure 3 - Footnote x <5 0 31 19 <5 Table Figure 3 - Footnote x 14 45
NT 16 12 Table Figure 3 - Footnote x <5 0 54 34 12 8 <5 Table Figure 3 - Footnote x
NU <5 Table Figure 3 - Footnote x 0 <5 0 <5 Table Figure 3 - Footnote x 0 <5 0 Table Figure 3 - Footnote x
Canada 2,966 1,107 52 1,689 436 10496 5272 741 4350 2047 12543
Percentage Table Figure 3 - Footnote 2 87.2% 37.3% 1.8% 56.9% 12.8% 83.7% 50.2% 7.1% 41.4% 16.3% 100.0%

To date this season, detailed information on age and type/subtype has been received for 10,686 cases. Adults aged 20-44 years accounted for the greatest proportion of influenza cases (Table 1). In week 8, children (aged 0-19 years) accounted for 41% of A(H1N1). Additionally, children aged 0-19 years accounted for 42% of influenza B confirmed cases to date this this season.

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 (February 21 to February 27, 2016) Cumulative (August 30, 2015 to February 27, 2016)
Influenza A B Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A UnSTable 1 - Footnote 3 Total A Total A(H1) pdm09 A(H3) A UnSTable 1 - Footnote 3 Total # %
<5 379 112 0 267 47 1650 932 45 673 215 1865 17.5%
5-19 264 124 0 140 78 1026 587 69 370 492 1518 14.2%
20-44 499 161 <5 Table 1 - Footnote x 59 2497 1505 107 885 484 2981 27.9%
45-64 450 129 <5 Table 1 - Footnote x 36 2266 1254 146 866 237 2503 23.4%
65+ 338 50 9 279 38 1577 605 288 684 242 1819 17.0%
Total 1930 576 14 1,340 258 9016 4883 655 3478 1670 10686 100.0%
PercentageTable 1 - Footnote 2 88.2% 29.8% 0.7% 69.4% 11.8% 84.4% 54.2% 7.3% 38.6% 15.6%    

For 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 from 41.6 per 1,000 patient visits in week 07, to 51.7 per 1,000 patient visits in week 08. In week 08, the highest ILI consultation rate was found in children 5-19 years of age (69.0 per 1,000) and the lowest was found in the ≥65 years age group (11.4 per 1,000) (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 07 for the 2015-16 season:
Age 0-4: 53.0; Age 5-19: 69.0; Age 20-64: 54.0; Age 65+: 11.4

Pharmacy Surveillance

During week 08, the proportion of prescriptions for antivirals increased to 88.4 antiviral prescriptions per 100,000 total prescriptions, which is lower than the five year historical average. The proportions were highest in children aged 2-18 years (233.4 per 100,000 total prescriptions).

Figure 5. Influenza-like-illness (ILI) consultation rates by age group and week, Canada, 2015-16

Figure 5

Note: Pharmacy sales data are provided to the Public Health Agency of Canada by Rx Canada Inc. and sourced from major retail drug chains representing over 3,000 stores nationwide (excluding Nunavut) in 85% of Health Regions. Data provided include the number of new antiviral prescriptions (for Tamiflu and Relenza) and the total number of new prescriptions dispensed by Province/Territory and age group.

* The average weekly proportion includes data from April 2011 to March 2015.

Figure 5 - Text Description

Proportion of antiviral prescriptions per 100,000 total prescriptions
Average National Rate (Yrs 10-11 to 14-15): 125.7.; Rate wk 08: 88.4
Proportion of antiviral prescriptions by age-group in week 07 for the 2015-16 season:
Infant: 121.4; child: 233.4; adult: 69.5; senior: 93.8

Influenza Outbreak Surveillance

In week 08, 38 new laboratory confirmed influenza outbreaks were reported: 25 in long-term care facilities (LTCF), seven in  institutions or community settings and six in hospitals. Of the outbreaks with known strains or subtypes, one outbreak was due to Influenza A(H3N2) and three outbreaks were due to influenza B.  Additionally, five ILI outbreaks were reported in schools.

To date this season,176 outbreaks have been reported. At week 08 in the 2014-15 season, 1,398 outbreaks were reported and in the 2013-14 season,134 outbreaks were reported.

Figure 6. Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2015-2016

Figure 6
Figure 6 - Text Description
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 0 0
37 0 1 1
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 2 0
51 1 1 0
52 1 0 2
1 0 2 1
2 0 2 0
3 1 4 1
4 4 8 3
5 8 6 3
6 8 10 3
7 2 17 8
8 6 25 7

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 08, 121 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Thirty-five hospitalizations were due to influenza A(H1N1) (29.0%), 18 were due to influenza B (15%) and the remainder were influenza A (UnS).

To date this season, 480 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by the IMPACT network: 390 hospitalized cases were due to influenza A and 90 cases were due to influenza B. The largest proportion of hospitalized cases were among children under the age of 2 years (37%). To date, 73 intensive care unit (ICU) admissions have been reported. ICU admissions were approximately equally distributed across ages with slightly smaller proportions of children 10-16 years admitted. Less than five influenza-associated deaths have been reported.

Table 2 - Cumulative numbers of peadiatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, Canada, 2015-16
Age Groups Cumulative (30 Aug. 2015 to 27 February 2016) 
Influenza A Influenza B Influenza A and B (#(%))
A Total A(H1) pdm09 A(H3) A (UnS) B Total
0-5m 42 13 <5 Table 2 - Footnote x 7 49 (10%)
6-23m 113 47 7 59 18 131 (27%)
2-4y 117 50 <5 Table 2 - Footnote x 25 142 (30%)
5-9y 85 29 <5 Table 2 - Footnote x 26 111 (23%)
10-16y 85 29 <5 Table 2 - Footnote x 26 47 (10%)
Total 390 153 18 219 90 480 (100%)

Figure 7. 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 7

Not included in Table 2 and Figure 7 are two IMPACT cases that were due to co-infections of influenza A and B.

Figure 7 - Text Description
Report week IMPACT CIRN-SOS
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 3 0
44 2 1
45 2 0
46 1 3
47 2 1
48 2 1
49 3 7
50 3 2
51 7 5
52 15 10
1 18 17
2 13 12
3 24 21
4 39 18
5 47 42
6 75 47
7 99 72
8 121 88

Adult Influenza Hospitalizations and Deaths

In week 08, 88 hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS). The largest proportion of hospitalizations were in adults 65+ years of age (45%) and due to influenza A (88%).

To date this season, 347 laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations have been reported by CIRN-SOS (Table 3). The majority of hospitalized cases were due to influenza A (86%) and the largest reported proption were among adults ≥65 years of age (50%). Forty-four intensive care unit (ICU) admissions have been reported and among those, 40 (91%) were due to influenza A. Twelve deaths have been reported this season.

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 27 Feb. 2016)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A(UnS) Total # (%)
16-20 <5 <5 Table 3 - Footnote x <5 Table 3 - Footnote x 3 (1%)
20-44 43 14 0 29 15 58 (17%)
45-64 103 25 <5 Table 3 - Footnote x 9 112 (32%)
65+ 149 24 16 109 22 171 (49%)
Unknown <5 Table 3 - Footnote x Table 3 - Footnote x <5 <5 3 (1%)
Total 300 65 18 217 47 347
% 86% 22% 6% 72% 14% 100%

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

Figure 8

Note: The number of hospitalizations reported through CIRN-SOS and IMPACT represents a subset of all influenza-associated adult and paediatric hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

x - Suppressed to prevent residual disclosure.

Figure 8 - Text Description
Age-group (years) Hospitalizations (n=344) ICU admissions (n=44) Deaths (n=12)
16-20 Table Figure 8 - Footnote x Table Figure 8 - Footnote x Table Figure 8 - Footnote x
20-44 Table Figure 8 - Footnote x Table Figure 8 - Footnote x Table Figure 8 - Footnote x
45-64 32.6% 43.2% Table Figure 8 - Footnote x
65+ 49.7% 40.9% 66.7%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 08, 276 hospitalizations have been reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (88%). The largest proportion of cases reported in week 08 were in adults 65+  years of age (29%) followed by adults 45-64 years (18%)

Since the start of the 2015-16 season, 1,632 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 1,451 hospitalizations (89%) were due to influenza A and 181 (11%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 91% (834/921) were influenza A(H1N1). The largest proportion (28%) of hospitalized cases were ≥65 years of age. One hundred seventy-eight  ICU admissions have been reported of which 161 (90%) were due to influenza A and 78 (44%) were in the 45-64 age group. A total of 36 deaths have been reported, all due to influenza A. The largest proportion  of deaths were reported in adults 65+ years of age,representing 47% of deaths.

Figure 9. Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group, Canada 2015-16

Figure 9
Figure 9 - Text Description
Age-group (years) Hospitalizations (n=1627) ICU admissions (n=178) Deaths (n=36)
0-4 21.7% 11.8% Table Figure 9 - Footnote x%
5-19 9.2% 7.3% 0.0%
20-44 15.2% 19.1% Table Figure 9 - Footnote x%
45-64 25.4% 43.8% 38.9%
65+ 28.5% 18.0% 47.2%

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 588 influenza viruses [129 A(H3N2), 307 A(H1N1) and 152 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 28 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 101 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): A total of 307 H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B: A total of 53 influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013. Ninety-nine 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 WHO has released the recommended composition of the northern hemisphere influenza vaccine for the 2016-2017 season. Trivalent vaccines are recommended to contain 1) an A/California/7/2009 (H1N1)pdm09-like virus 2) an A/HongKong/4801/2014 (H3N2)-like virus, and 3) a B/Brisbane/60/2008-like virus (Victoria lineage). Quadrivalent vaccines are recommended to additionally contain a B/Phuket/30732013-like virus (Yamagata lineage).

The recommended components for the 2015-2016 northern hemisphere trivalent influenza vaccine include: an A/California/7/2009(H1N1)pdm09-like virus, an A/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  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 500 influenza viruses for resistance to oseltamivir, 547 for resistance to zanamivir and 418 for resistance to amantadine. All but one virus tested  for resistance were sensitive to oseltamivir. All viruses tested for restistance were sensitive to zanamavir.  A total of 417 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) 120 0 123 0 131 130 (99.2%)
A (H1N1) 254 1 283 0 287 287 (100%)
B 126 0 141 0 NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 500 1 547 0 418 417

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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