FluWatch report: March 20 to March 26, 2016 (week 12)

Overall Summary

  • For the second consecutive week, influenza activity continued to decrease across Canada.
  • All regions of Canada reported sporadic or localized influenza activity.
  • The number of positive influenza B tests reported continues to increase, but still accounted for only 30% of positive influenza tests in week 12
  • Adults greater than 65 years of age accounted for the majority of hospitalizations in week 12 and account for the largest proportion of hospitalizations to date this season.
  • Hospitalizations, ICU admissions and deaths among the pediatric population, while declining, remain above expected levels based on the past several influenza seasons.
  • 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: 2016-04-01

Influenza/Influenza-like Illness Activity (geographic spread)

In week 12, influenza activity was present in all regions of Canada. A total of 21 regions reported localized activity levels across the country. Sporadic influenza/ILI activity was reported in 32 regions across Canada.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, week 12

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 12, influenza activity was present in all regions of Canada. A total of 21 regions reported localized activity levels across the country. Sporadic influenza/ILI activity was reported in 32 regions across Canada.

Laboratory Confirmed Influenza Detections

In week 12, the percent positive for influenza continued to decrease from the previous week [from 31% in week 11 to 30% in week 12 (Figure 2)]. Compared to the previous five seasons, the percent positive (30%) reported in week 12 was above the five year average for that week and exceeded the expected levels (range 11.3%-19.8%). With the late start to the 2015-16 influenza season, these above normal levels are not unexpected.

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

In week 12, the percent positive for influenza continued to decreased from the previous week [from 31% in week 11 to 30% in week 12.

In week 12, there were 2,882 positive influenza tests reported. To date, 81% of influenza detections have been influenza A and among those subtyped, the vast majority have been influenza A(H1N1) [91% (9630/10584]. The number of positive influenza B tests reported is accounting for an increasing proportion of all positive influenza tests reported; this week, influenza B positive tests accounted for 30% of all positive tests.

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 20 to March 26, 2016) Cumulative (August 30, 2015 to March 26, 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
Table Figure 3 - Footnote 1

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

Return to Table Figure 3 - Footnote 1 referrer

Table Figure 3 - Footnote 2

Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections.

Return to Table Figure 3 - Footnote 2 referrer

Table Figure 3 - Footnote UnS

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to first Table Figure 3 - Footnote UnS referrer

Table Figure 3 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table Figure 3 - Footnote x referrer

BC 141 70 <5 Table Figure 3 - Footnote x 51 1583 723 331 529 1030 2541
AB 153 88 <5 Table Figure 3 - Footnote x 183 3657 3334 165 158 1188 4845
SK 56 30 <5 Table Figure 3 - Footnote x 33 1688 1336 41 311 383 2071
MB 51 12 <5 Table Figure 3 - Footnote x 9 765 159 36 570 77 842
ON 601 215 17 369 282 6563 2887 337 3339 1480 8043
QC 823 30 <5 Table Figure 3 - Footnote x 293 7350 880 5 6465 1040 8390
NB 153 16 0 137 7 576 54 <5 Table Figure 3 - Footnote x 22 598
NS 22 0 0 22 <5 191 0 <5 190 <5 195
PE <5 <5 <5 0 0 51 50 <5 Table Figure 3 - Footnote x Table Figure 3 - Footnote x 51
NL 0 0 0 0 0 285 58 <5 Table Figure 3 - Footnote x 9 294
YT 6 <5 0 <5 <5 65 39 <5 Table Figure 3 - Footnote x 18 83
NT 6 <5 <5 0 <5 150 109 28 13 8 158
NU 6 0 0 6 0 10 <5 Table Figure 3 - Footnote x 9 14 24
Canada 2021 471 29 1521 861 22934 9630 954 12350 5273 28207
Percentage Table Figure 3 - Footnote 2 70% 23% 1% 75% 30% 81% 42% 4% 54% 19% 100%

To date this season, detailed information on age and type/subtype has been received for 24,173 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 reporting Table 1 - Footnote 1, Canada, 2015-16
Age groups (years) Weekly (March 20 to March 26, 2016) Cumulative (August 30, 2015 to March 26, 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 # %
Table 1 - Footnote 1

Table 1 includes specimens for which demographic information was reported. These represent a subset of all positive influenza cases reported.

Return to Table 1 - Footnote 1 referrer

Table 1 - Footnote 2

Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections.

Return to Table 1 - Footnote 2 referrer

Table 1 - Footnote 3

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to first Table 1 - Footnote 3 referrer

Table 1 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table 1 - Footnote x referrer

<5 259 15 <5 Table 1 - Footnote x 112 3794 1564 62 2168 710 4511 19%
5-19 83 11 <5 Table 1 - Footnote x 148 2055 931 89 1035 1351 3417 14%
20-44 235 26 <5 Table 1 - Footnote x 122 4893 2404 138 2351 1146 6048 25%
45-64 303 38 <5 Table 1 - Footnote x 62 5172 2310 172 2690 521 5698 24%
65+ 293 38 7 248 90 3827 1301 368 2158 667 4499 19%
Total 1173 128 15 1030 534 19741 8510 829 10402 4395 24173 100%
PercentageTable 1 - Footnote 2 69% 11% 1% 88% 31% 82% 43% 4% 53% 18%    

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 53.6 per 1,000 patient visits in week 11, to 43.6 per 1,000 patient visits in week 12.The highest ILI consultation rate was found in the 5-19 years age group (84.2 per 1,000) and the lowest was found in the ≥65 years age group (14.7 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 12 for the 2015-16 season:

  • Age 0-4: 35.6;
  • Age 5-19: 84.2;
  • Age 20-64: 37.9;
  • Age 65+: 14.7

Pharmacy Surveillance

During week 12, the proportion of prescriptions for antivirals decreased to 72.9 antiviral prescriptions per 100,000 total prescriptions, which is slightly higher than the five year historical average for week 12. The proportion of prescriptions for antivirals remains highest among children. In week 12, the proportion reported among children was 199.3 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): 73.3.;
  • Rate wk 12: 123.5

Proportion of antiviral prescriptions by age-group in week 12 for the 2015-16 season:

  • Infant: 148.1;
  • Child: 199.3;
  • Adult: 71.0;
  • Senior: 65.3

Influenza Outbreak Surveillance

In week 12, 27 new laboratory confirmed influenza outbreaks were reported: 13 in long-term care facilities (LTCF), nine in hospitals and 5 in institutions or community settings. Of the outbreaks with known strains or subtypes, one outbreak was due to influenza B, three outbreaks were due to influenza A(H1N1) and three were due to influenza A(Uns). Additionally, one ILI outbreak was reported in a school.

To date this season, 330 outbreaks have been reported. At week 12 in the 2014-15 season, 1,587 outbreaks were reported and in the 2013-14 season,170 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
8 6 27 7
9 13 24 8
10 9 23 14
11 2 21 4
12 9 13 5

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In week 12, 85 hospitalizations were reported by the the Immunization Monitoring Program Active (IMPACT) network, a decrease from the previous three weeks (Figure 7). The largest proportion of hospitalizations were in children aged 5-9 years, accounting for 27% of the hospitalizations. The majority of hospitalizations were due to influenza A (65%).

To date this season, 1007 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations have been reported by  the IMPACT network: 783 hospitalized cases were due to influenza A and 224 cases were due to influenza B. The greatest proportion of hosptalization cases were in children aged 6-23 months and children 2-4 years, each accounting for 28% of hospitalizations. To date, 169 intensive care unit (ICU) admissions have been reported. Children aged 2 to 4 and 5 to 9 years each accounted for 27% of ICU admissions. A total of 135 ICU cases (80%) reported to have at least one underlying condition or comorbidity. Seven 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 26 March 2016)
Influenza A Influenza B Influenza A and B (#(%))
A Total A(H1) pdm09 A(H3) A (UnS) B Total
Table 2 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table 2 - Footnote x referrer

0-5m 106 32 <5 Table 2 - Footnote x 17 123 (12%)
6-23m 233 69 7 157 49 282 (28%)
2-4y 226 75 <5 Table 2 - Footnote x 53 279 (28%)
5-9y 166 45 <5 Table 2 - Footnote x 73 239 (24%)
10-16y 52 18 <5 Table 2 - Footnote x 32 84 (8%)
Total 783 239 19 525 224 1007 (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 2
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 13
3 24 26
4 39 19
5 48 42
6 76 52
7 108 86
8 148 119
9 147 102
10 148 121
11 112 100
12 85 57

Adult Influenza Hospitalizations and Deaths

In week 12, 57 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 (53%) and due to influenza A (81%).

To date this season, 791 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 proportion were among adults ≥65 years of age (48%). One hundred and twelve intensive care unit (ICU) admissions have been reported and among those, 101 (90%) were due to influenza A. A total of 69 ICU cases (62%) reported to have at least one underlying condition or comorbidity. Twenty-seven deaths have been reported this season with the majority of deaths reported in adults ≥65 years of age (67%).

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 26 March 2016)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A(UnS) Total # (%)
Table 3 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table 3 - Footnote x referrer

16-20 <5 <5 0 <5 0 4 (1%)
20-44 106 33 <5 Table 3 - Footnote x 21 127 (16%)
45-64 245 69 <5 Table 3 - Footnote x 25 270 (34%)
65+ 321 73 21 227 62 383 (48%)
Unknown 6 <5 0 <5 <5 7 (1%)
Total 682 182 25 475 109 791
% 86% 27% 4% 70% 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=784) ICU admissions (n=112) Deaths (n=27)
Table Figure 8 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table Figure 8 - Fo2tn273x referrer

16-20 <5 <5 <5
20-44 Table Figure 8 - Footnote x Table Figure 8 - Footnote x Table Figure 8 - Footnote x
45-64 34.4% 41.1% 25.9%
65+ 48.9% 35.7% 66.7%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 12, 273 hospitalizations were reported from participating provinces and territoriesFootnote *. The majority of hospitalizations were due to influenza A (78%). The largest proportion of cases reported in week 12 were in adults 65+  years of age (31%).

Since the start of the 2015-16 season, 3,491 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 3,024 hospitalizations (87%) were due to influenza A and 467 (13%) were due to influenza B. Among cases for which the subtype of influenza A was reported, 93% (1442/1554) were influenza A(H1N1). The largest proportion (30%) of hospitalized cases were ≥65 years of age, followed closely by adults 45-64 years of age (27%). Three hundred and eighty nine ICU admissions have been reported of which 225 (58%) were due to influenza A(H1N1) and 175 (45%) were in the 45-64 age group. A total of 140 deaths have been reported; all but 10 were associated with influenza A. Adults ≥65 years of age each represented 46% of reported deaths.

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

Figure 9

x - Suppressed to prevent residual disclosure.

Figure 9 - Text Description
Age-group (years) Hospitalizations (n=3491) ICU admissions (n=389) Deaths (n=140)
Table Figure 9 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table Figure 9 - Footnote x referrer

0-4 20.3% 10.0% Table Figure 9 - Footnote x%
5-19 9.4% 5.9% Table Figure 9 - Footnote x%
20-44 14.2% 18.5% 9.3%
45-64 26.7% 45.0% 37.1%
65+ 29.5% 20.6% 46.4%

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 1312 influenza viruses [149 A(H3N2), 775 A(H1N1) and 388 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 35 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 114 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 775 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 104 influenza B viruses characterized  were antigenically similar to the vaccine strain B/Phuket/3073/2013. A total of 284 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 904 influenza viruses for resistance to oseltamivir, 826 for resistance to zanamivir and 940 influenza viruses for resistance to amantadine. All but seven tested viruses were sensitive to oseltamivir. The seven H1N1 viruses resistant to oseltamivir had a H275Y mutation. All viruses tested for resistance were sensitive to zanamivir. All but one 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 (%)
Table 4 - Footnote *

NA - not applicable

Return to first Table 4 - Footnote * referrer

A (H3N2) 137 0 134 0 160 159 (99.4%)
A (H1N1) 545 7 479 0 780 780 (100%)
B 222 0 213 0 NATable 4 - Footnote * NATable 4 - Footnote *
Total 904 7 826 0 940 939

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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