FluWatch report: February 14, 2016 – February 20, 2016 (week 7)

Overall Summary

  • Overall in week 07, influenza confirmations continued to increase slightly with greater geographic spread
  • Pediatric hospitalizations reported by the IMPACT network continue to substantially increase, reaching 94 hospitalizations in week 07.
  • Young/middle age adults are accounting for an increasing proportion of hospitalizations and laboratory confirmed cases as reported by participating provinces and territories.
  • An increase in the number of outbreaks was reported in week 07 with the majority of outbreaks reported in long-term care facilities. 
  • Influenza A(H1N1) remains the most common influenza subtype circulating in Canada.
  • The World Health Organization has released their recommended composition of influenza virus vaccines for use in the 2016-2017 northern hemisphere influenza season.
  • 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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Organization:
Date published: 2016-02-26

Influenza/Influenza-like Illness Activity (geographic spread)

In week 07, a larger proportion of regions reported elevated activity levels. A total of 29 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 15 regions in Canada and widespread activity was reported in one region of Quebec.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, Week 07

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 07, a larger proportion of regions reported elevated activity levels. A total of 29 regions across Canada reported sporadic influenza/ILI activity. Localized activity was reported in 15 regions in Canada and widespread activity was reported in one region of Quebec. 

Laboratory Confirmed Influenza Detections

Laboratory confirmed influenza detections continued to increase. The percent positive for influenza increased from 25% in week 06 to 29% in week 07 (Figure 2). Compared to the previous five seasons, the percent positive (29%) reported in week 07 was above the five year average for that week and exceeded the expected levels (range 13.0%-19.7%). 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 25% in week 06 to 29% in week 07.

In week 07, there were 2,453 positive influenza tests reported. Influenza A(H1N1) was the most common subtype detected. The majority of influenza detections were reported in the provinces of AB, ON and QC. Increased detections of influenza in the  central and eastern provinces have been noted in the last few weeks. To date, 83% of influenza detections have been influenza A and among those subtyped, the majority have been influenza A(H1N1) [85% (3963/4654)].

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 14 to February 20, 2016) Cumulative (August 30, 2015 to February 20, 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 144 70 17 57 121 902 275 286 341 714 1616
AB 458 327 5 134 87 2148 1870 118 160 375 2523
SK 91 91 <5 x 24 622 405 12 205 82 704
MB 34 8 5 21 <5 113 56 31 26 10 123
ON 434 184 12 238 91 1814 979 217 618 267 2081
QC 669 146 <5 x 31 1574 209 <5 x 120 1694
NB 25 <5 0 21 <5 99 21 <5 77 <5 103
NS 12 0 0 12 <5 41 0 <5 40 0 41
PE 7 7 0 0 0 34 34 0 0 0 34
NL 27 14 0 13 0 48 29 <5 17 <5 51
YT 5 <5 0 <5 <5 24 13 <5 7 14 38
NT 6 <5 0 <5 <5 38 22 12 <5 2 40
NU 0 0 0 0 0 0 0 0 0 0 0
Canada 2,075 920 41 1,114 378 7517 3963 691 2863 1582 9099
Percentage Table Figure 3 - Footnote 2 84.6% 44.3% 2.0% 53.7% 15.4% 82.6% 52.7% 9.2% 38.1% 17.4% 100.0%

To date this season, detailed information on age and type/subtype has been received for 7,622 cases. Adults aged 20-44 years accounted for the greatest proportion of influenza cases (Table 1). Adults aged 20-44 and 45-64 years accounted for 57% of reported influenza A(H1N1) cases. Children 5-19 years and adults 20-44 years accounted for 60% 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 (February 14 to February 20, 2016) Cumulative (August 30, 2015 to February 20, 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 # %
<5 289 129 <5 xTable 1 - Footnote 4 36 1089 681 42 366 157 1246 16.3%
5-19 160 59 <5 xTable 1 - Footnote 4 51 716 439 65 212 387 1103 14.5%
20-44 413 174 <5 xTable 1 - Footnote 4 76 1812 1153 101 558 402 2214 29.0%
45-64 357 142 <5 xTable 1 - Footnote 4 37 1598 926 138 534 188 1786 23.4%
65+ 239 82 10 147 33 1084 429 264 391 189 1273 16.7%
Total 1,458 586 17 855 233 6299 3628 610 2061 1323 7622 100.0%
PercentageTable 1 - Footnote 2 86.2% 40.2% 1.2% 58.6% 13.8% 82.6% 57.6% 9.7% 32.7% 17.4%    

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 decreased from the previous week from 51.0 per 1,000 patient visits in week 06, to 41.6 per 1,000 patient visits in week 07. In week 07, the highest ILI consultation rate was found in adults 20-64 years of age (47.4 per 1,000) and the lowest was found in the ≥65 years age group (8.8 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 07 for the 2015-16 season:
Age 0-4: 31.5; Age 5-19: 46.6; Age 20-64: 47.4; Age 65+: 8.8

Pharmacy Surveillance

During week 07, the proportion of prescriptions for antivirals increased to 80.2 antiviral prescriptions per 100,000 total prescriptions, which is lower than the five year historical average (5). The rates were highest in children (173.1 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): 174.1; Rate wk 07: 80.2
Proportion of antiviral prescriptions by age-group in week 07 for the 2015-16 season:
Infant: 37.5; child: 38.9; adult: 29.2; senior: 5.4

Influenza Outbreak Surveillance

In week 07, 27 new laboratory confirmed influenza outbreaks were reported: 17 in long-term care facilities (LTCF), eight in  institutions or community settings and two in hospitals. Of the outbreaks with known strains or subtypes, two outbreaks were due to Influenza A(H1N1) and one outbreak was due to influenza B.  Additionally, two ILI outbreaks were reported in schools.

To date this season,131 outbreaks have been reported. At week 07 in the 2014-15 season, 1,367 outbreaks were reported and in the 2013-14 season,118 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 6 3
5 8 6 3
6 8 10 3
7 2 17 8

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 07, 94 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network (Figure 7). Eighteen hospitalizations were due to influenza A(H1N1) (19%), 18 were due to influenza B (19%) and the remainder were influenza A (UnS).

To date this season, 350 laboratory-confirmed influenza-associated paediatric (≤16 years of age) hospitalizations have been reported by  the IMPACT network: 281 hospitalized cases were due to influenza A and 69 cases were due to influenza B. The largest proportion of hospitalized cases were among children aged 2-4 years (31%). To date, 55 intensive care unit (ICU) admissions have been reported. The largest proportion of ICU admissions were reported in children 2-9 years (51%). 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 20 February 2016) 
Influenza A Influenza B Influenza A and B (#(%))
A Total A(H1) pdm09 A(H3) A (UnS) B Total
0-5m 37 11 <5 xTable 2 - Footnote 1 6 43 (12%)
6-23m 74 34 <5 xTable 2 - Footnote 1 13 87 (25%)
2-4y 88 38 <5 xTable 2 - Footnote 1 19 107 (31%)
5-9y 59 22 0 37 21 80 (23%)
10-16y 23 10 <5 xTable 2 - Footnote 1 10 33 (9%)
Total 281 115 11 155 69 350 (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 2
51 7 4
52 15 9
1 18 17
2 13 12
3 24 18
4 39 18
5 47 40
6 75 41
7 94 51

Adult Influenza Hospitalizations and Deaths

In week 07, 51 hospitalizations were reported by the Canadian Immunization Research Network Serious Outcome Surveillance (CIRN-SOS). The majority of hospitalizations were in adults 45-64 and 65+ years of age (84%) and due to influenza A (93%).

To date this season, 225 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 (84%) and the largest reported proption were among adults ≥65 years of age (50%). Twenty-four intensive care unit (ICU) admissions have been reported and among those, 22 (92%) were due to influenza A. Six 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 20 Feb. 2016)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A(UnS) Total # (%)
16-20 <5 <5 <5 <5 <5 <5 (x%)
20-44 23 8 0 15 13 36 (16%)
45-64 66 19 <5 x 7 73 (32%)
65+ 97 16 14 67 15 112 (50%)
Unknown <5 <5 <5 <5 <5 <5 (x%)
Total 189 44 16 129 36 225
% 84% 23% 8% 68% 16% 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.

Figure 8 - Text Description

Age-group (years) Hospitalizations (n=223) ICU admissions (n=24) Deaths (n=6)
16-20 xTable figure 8 - Footnote 1 0.0% x
20-44 xTable figure 8 - Footnote 1 20.8% x
45-64 32.7% 41.7% x
65+ 50.2% 37.5% x

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 07, 222 hospitalizations have been reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (89%). The largest proportion of cases reported in week 07 were in children 0-19 years (39%).

Since the start of the 2015-16 season, 1,235 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 1,105 hospitalizations (90%) were due to influenza A and 56 (10%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 89% (650/727) were influenza A(H1N1). The majority (29%) of hospitalized cases were ≥65 years of age. One hundred thirty-one  ICU admissions have been reported of which 118 (90%) were due to influenza A and 57 (44%) were in the 45-64 age group. A total of 30 deaths have been reported, all due to influenza A. The largest proportion  of deaths were reported in adults 45-64 and 65+ of age,representing 86% 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=1235) ICU admissions (n=131) Deaths (n=30)
0-4 20.6% 10.7% x%
5-19 8.0% 6.9% x%
20-44 15.8% 20.6% 6.7%
45-64 26.6% 43.5% 43.3%
65+ 28.9% 18.3% 43.3%

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 521 influenza viruses [122 A(H3N2), 268 A(H1N1) and 131 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 27 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 95 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): Two hundred and sixty-eight H1N1 viruses characterized were antigenically similar to A/California/7/2009, the A(H1N1) component of the 2015-16 influenza vaccine.

Influenza B:Forty-six influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013. Eighty-five 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 /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 476 influenza viruses for resistance to oseltamivir and zanamivir and 336 influenza for resistance to amantadine. Close to 100% of all viruses were sensitive to oseltamivir. All viruses tested for restistance were sensitive to zanamavir.  A total of 335 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) 116 0 (0%) 116 0 (0%) 126 125 (99.2%)
A (H1N1) 230 <5 (x%) 230 0 (0%) 210 210 (100%)
B 119 0 (0%) 119 0 (0%) NA Table 4 - Footnote * NA Table 4 - Footnote *
TOTAL 465 <5 (x%) 465 0 (0%) 336 335 (99.7%)

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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