FluWatch report: March 6 to March 12, 2016 (week 10)

Overall Summary

  • Influenza activity continues to increase and is typical of peak season levels. The Eastern provinces of Canada accounted for the majority of influenza activity nationally.
  • Nearly all regions in Canada are reporting sporadic or localized influenza activity.
  • In week 10, 46 outbreaks were reported and the majority of outbreaks were in long-term care facilities.
  • Adults greater than 45 years of age accounted for the majority of hospitalizations in week 10.
  • Hospitalizations and ICU admissions among the pediatric population continue to be above typical peak season levels.
  • A Canadian study reported an interim estimate of vaccine effectiveness of 64% against influenza A(H1N1) in Canada. This estimate suggests that the 2015-16 northern hemisphere vaccine has provided good protection against the influenza A(H1N1) virus, the most common circulating influenza virus.
  • For more information on the flu, see our Flu(influenza) web page.

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Organization: Public Health Agency of Canada

Date published: 2016-03-11

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 10, influenza activity was present in almost every region in Canada. A total of 24 regions reported localized activity levels with the majority in the eastern regions of Canada. Sporadic influenza/ILI activity was reported in 27 regions across Canada.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, week 10

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 10, influenza activity was present in almost every region in Canada. A total of 24 regions reported localized activity levels with the majority in the eastern regions of Canada. Sporadic influenza/ILI activity was reported in 27 regions across Canada.

Laboratory Confirmed Influenza Detections

The percent positive for influenza increased slightly from the previous week [from 34% in week 09 to 36% in week 10 (Figure 2)]. This small increase from the previous week may suggest that the influenza season is near its peak. Compared to the previous five seasons, the percent positive (36%) reported in week 10 was above the five year average for that week and exceeded the expected levels (range 12.8%-18.3%). 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 slightly from the previous week, from 34% in week 09 to 36% in week 10.

In week 10, there were 4,359 positive influenza tests reported. The Atlantic provinces reported the greatest percent increase (37%) in the number of positive influenza tests compared to the previous week. To date, 84% of influenza detections have been influenza A and among those subtyped, the vast majority have been influenza A(H1N1) [90% (7818/8679)].

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 (March 6 to March 12, 2016) Cumulative (August 30, 2015 to March 12, 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 192 159 17 16 68 1333 595 328 410 929 2198
AB 294 254 6 45 152 3238 2977 154 107 803 4041
SK 170 22 0 148 47 1563 930 19 614 244 1807
MB 211 10 <5 Table Figure 3 - Footnote x 21 606 128 35 443 41 647
ON 983 484 21 478 207 4705 2273 293 2139 799 5504
QC 1,352 150 0 1,202 191 5416 696 <5 Table Figure 3 - Footnote x 523 5939
NB 86 0 0 86 <5 294 27 <5 Table Figure 3 - Footnote x <5 303
NS 48 0 0 48 <5 135 0 <5 Table Figure 3 - Footnote x <5 138
PE 6 6 0 0 0 44 44 0 0 0 44
NL 69 <5 0 Table Figure 3 - Footnote x <5 218 50 <5 Table Figure 3 - Footnote x 8 226
YT 14 Table Figure 3 - Footnote x 0 <5 0 52 31 <5 Table Figure 3 - Footnote x 17 69
NT 17 11 <5 Table Figure 3 - Footnote x <5 Table Figure 3 - Footnote x 67 20 6 <5 97
NU 0 0 0 0 10 <5 0 0 <5 Table Figure 3 - Footnote x 14
Canada 3442 1111 46 2285 704 17699 7818 861 9020 3392 21091
Percentage Table Figure 3 - Footnote 2 83% 32% 1% 66% 17% 84% 44% 5% 51% 16% 100%

To date this season, detailed information on age and type/subtype has been received for 18,729 cases. Adults aged 20-44 years accounted for the greatest proportion of influenza cases, followed closely by adults aged 45-64 (Table 1). Adults aged 20-44 and 45-64 years accounted for 55% of reported influenza A(H1N1) cases. Children 5-19 years and adults 20-44 years accounted for 57% of all influenza B cases reported.

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 (March 6 to March 12, 2016) Cumulative (August 30, 2015 to March 12, 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 # %
<5 489 118 0 371 106 2973 1392 52 1529 457 3430 18%
5-19 169 44 <5 Table 1 - Footnote x 167 1671 851 77 743 901 2572 14%
20-44 587 180 <5 Table 1 - Footnote x 133 4112 2175 130 1907 809 4921 26%
45-64 722 211 <5 Table 1 - Footnote x 61 4087 1963 159 1965 385 4472 24%
65+ 549 140 18 391 81 2899 1085 354 1400 435 3334 18%
Total 2516 693 29 1794 548 15742 7466 772 7504 2987 18729 100%
PercentageTable 1 - Footnote 2 82% 28% 1% 71% 18% 84% 47% 5% 48% 16%    

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 63.3 per 1,000 patient visits in week 09, to 75.6 per 1,000 patient visits in week 10.The highest ILI consultation rate was found in the 5-19 years of age group (151.5 per 1,000) and the lowest was found in the ≥65 years age group (21.8 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 10 for the 2015-16 season:
Age 0-4: 82.5; Age 5-19: 151.5; Age 20-64: 63.2; Age 65+: 21.8

Pharmacy Surveillance

During week 10, the proportion of prescriptions for antivirals increased to 144.7 antiviral prescriptions per 100,000 total prescriptions, which is higher than the five year historical average for week 10. The proportion of antiviral prescriptions among infants more than doubled from week 09. The highest proportion of prescriptions for antivirals remains highest among children. In week 10, the proportion reported among children was 341.8 per 100,000 total prescriptions.

Figure 5. Proportion of prescription sales for influenza antivirals 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[oseltamivir] and Relenza [zanamivir]) 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): 96.8.; Rate wk 10: 144.8
Proportion of antiviral prescriptions by age-group in week 10 for the 2015-16 season:
Infant: 234.6; child: 341.8; adult: 104.5; senior: 165.4

Influenza Outbreak Surveillance

In week 10, 46 new laboratory confirmed influenza outbreaks were reported: 23 in long-term care facilities (LTCF), nine in hospitals and 14 in institutions or community settings. Of the reported LTCF outbreaks, 13 were due to influenza A(UnS), six due to influenza A(H1N1), one due to influenza A(H3N2) and three due to influenza B. For the remaining outbreaks in hospitals and community settings: two were due to influenza A(H3N2), one due to influenza A(H1N1), seven due to influenza A(UnS) and three due to influenza B. Additionally, three ILI outbreaks were reported in schools.

To date this season, 274 outbreaks have been reported. At week 10 in the 2014-15 season, 1,376 outbreaks were reported and in the 2013-14 season,147 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 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 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 27 7
9 13 24 8
10 9 23 14

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 10, 134 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network, down slightly from the previous two weeks (Figure 7). The largest proportion of hospitalizations were in children aged 6-23 months (34%) and the majority of hospitalizations were due to influenza A (72%).

To date this season, 792 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations have been reported by the IMPACT network: 641 hospitalized cases were due to influenza A and 151 cases were due to influenza B. The greatest proportion of hosptalizations cases were in children aged 6-23 months and children 2-4 years, each accounting for 28% of hospitalizations. To date, 136 intensive care unit (ICU) admissions have been reported. Children aged 2 to 4 years accounted for 28% of ICU admissions. A total of 71 ICU cases (52%) reported to have at least one underlying condition or comorbidity. 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 12 March 2016) 
Influenza A Influenza B Influenza A and B (#(%))
A Total A(H1) pdm09 A(H3) A (UnS) B Total
0-5m 85 27 <5 Table 2 - Footnote x 11 96 (12%)
6-23m 186 59 7 120 35 221 (28%)
2-4y 188 68 <5 Table 2 - Footnote x 37 225 (28%)
5-9y 135 42 <5 Table 2 - Footnote x 47 182 (23%)
10-16y 47 16 <5 Table 2 - Footnote x 21 68 (9%)
Total 641 212 19 410 151 792 (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 1 0
44 0 1
45 2 0
46 1 3
47 2 1
48 2 1
49 3 7
50 3 3
51 6 5
52 15 11
1 18 19
2 13 12
3 24 24
4 39 19
5 48 42
6 75 51
7 108 83
8 149 108
9 145 87
10 134 89

Adult Influenza Hospitalizations and Deaths

In week 10, 79 hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS) (Figure 7). The largest proportion of hospitalizations were in adults 65+ years of age (56%) and due to influenza A (88%).

To date this season, 566 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 (88%) and the largest reported proportion were among adults ≥65 years of age (48%). Seventy-four intensive care unit (ICU) admissions have been reported and among those, 64 (86%) were due to influenza A. A total of 38 ICU cases (51%) reported to have at least one underlying condition or comorbidity. Nineteen 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 12 March 2016)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A(UnS) Total # (%)
16-20 <5 <5 0 <5 0 <5
20-44 81 22 <5 Table 3 - Footnote x 18 99 (17%)
45-64 166 37 <5 Table 3 - Footnote x 17 183 (32%)
65+ 240 40 17 183 34 274 (48%)
Unknown Table 3 - Footnote x <5 0 <5 0 <5
Total 497 105 21 371 69 566
% 88% 21% 4% 75% 12% 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=560) ICU admissions (n=74) Deaths (n=19)
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 32.7% 40.5% 21.1%
65+ 48.9% 33.8% 73.7%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 10, 399 hospitalizations were reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (89%). The largest proportion of cases reported in week 10 were in adults 65+ years of age (32%).

Since the start of the 2015-16 season, 2,598 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 2,291 hospitalizations (88%) were due to influenza A and 307 (12%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 92% (1166/1270) were influenza A(H1N1). The largest proportion (29%) of hospitalized cases were ≥65 years of age, followed closely by adults 45-64 years of age (26%). Two hundred and ninety ICU admissions have been reported of which 181 (62%) were due to influenza A(H1N1) and 128 (44%) were in the 45-64 age group. A total of 89 deaths have been reported, all but two were due to influenza A. Adults 45-64 and ≥65 years of age each represented 40% of reported 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=2598) ICU admissions (n=290) Deaths (n=89)
0-4 21.3% 10.7% Table Figure 9 - Footnote x%
5-19 9.4% 6.6% Table Figure 9 - Footnote x%
20-44 14.4% 29.3% 11.2%
45-64 25.9% 44.1% 40.4%
65+ 29.0% 19.3% 40.4%

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 994 influenza viruses [140 A(H3N2), 611 A(H1N1) and 243 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 29 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 111 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 611 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 77 influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. A total of 166 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 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 729 influenza viruses for resistance to oseltamivir, 730 for resistance to zanamivir and 604 influenza viruses for resistance to amantadine. All but six tested viruses were sensitive to oseltamivir. The six H1N1 viruses resistant to oseltamivir had a H275Y mutation. All viruses tested for resistance were sensitive to zanamivir. A total of 603 influenza A viruses 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) 126 0 126 0 141 140 (99.3%)
A (H1N1) 415 6 416 0 463 463 (100%)
B 188 0 188 0 NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 729 6 730 0 604 603

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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