FluWatch report: June 19 to July 16, 2016 (weeks 25-28)

Overall Summary

  • Overall, influenza activity is at interseasonal levels and continues to decrease across Canada.
  • For the first time since week 15, influenza A accounted for the majority of influenza detections.
  • Sporadic activity is being reported in some parts of Canada; however, the majority of regions are reporting no influenza activity.
  • No laboratory-confirmed influenza outbreaks have been reported since week 22 (beginning of June).
  • Influenza-associated hospitalizations continue to decrease. Two hospitalizations were reported in week 28.
  • For more information on the flu, see our Flu (influenza) web page.
Many thanks to all the sentinels participating in our influenza-like illness surveillance network. Your hard work is greatly appreciated!

If you are a primary health care practitioner (General Practitioner, Nurse Practitioner or Registered Nurse) interested in becoming a FluWatch sentinel for the 2016-17 influenza season, please contact us at FluWatch@phac-aspc.gc.ca

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Date published: 2016-07-22

Influenza/Influenza-like Illness Activity (geographic spread)

In weeks 25 to 28, influenza activity declined. Sporadic activity was reported in seven regions across six provinces (BC, AB, ON, QC, NB and NU). A total of 37 regions reported no influenza activity.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, week 28

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 weeks 25 to 28, influenza activity declined. Sporadic activity was reported in seven regions across six provinces (BC, AB, ON, QC, NB and NU). A total of 37 regions reported no influenza activity.

Laboratory Confirmed Influenza Detections

In weeks 25-28, the percentage of tests positive for influenza continued to decrease [from 1.2% in week 25 to 0.6% in week 28]. Compared to the previous five seasons, the percent positive (0.6%) reported in week 28 was within expected levels (confidence interval 0.4-0.7%) and remains at interseasonal 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

In weeks 25-28, the percentage of tests positive for influenza continued to decrease [from 1.2% in week 25 to 0.6% in week 28].

Nationally in weeks 25-28, there were 59 positive influenza tests reported. Influenza A accounted for the majority of influenza detections, representing 68% of detections in weeks 25-28. To date, 72% of influenza detections have been influenza A and among those subtyped, the vast majority have been influenza A(H1N1) [91% (11074/12213)].

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
Weeks 25-28 (June 19 to July 16, 2016) Cumulative (August 30, 2015 to July 16, 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

Cumulative data includes updates to previous weeks.
BC 16 5 5 6 0 2081 1033 367 681 1168 3169
AB <5 <5 <5 0 <5 3966 3642 210 114 1674 5640
SK 0 0 0 0 0 2337 1514 47 776 829 3166
MB 0 0 0 0 <5 899 186 38 675 241 1140
ON 9 <5 <5 <5 <5 7696 3268 419 4009 2864 10560
QC 8 0 0 8 9 8979 1026 8 7945 3867 12846
NB <5 <5 0 <5 <5 1175 101 5 1069 154 1329
NS 0 0 0 0 0 302 0 <5 Table Figure 3 - Footnote x 11 313
PE 0 0 0 0 0 66 54 12 0 <5 69
NL 0 0 0 0 0 472 101 <5 Table Figure 3 - Footnote x 28 500
YT 0 0 0 0 0 58 53 <5 <5 19 77
NT 0 0 0 0 0 122 90 27 5 20 142
NU 0 0 0 0 <5 25 6 0 19 34 59
Canada 40 11 10 19 19 28178 11074 1139 15965 10912 39090
Percentage Table Figure 3 - Footnote 2 68% 28% 25% 48% 32% 72% 39% 4% 57% 28% 100%

To date this season, detailed information on age and type/subtype has been received for 33,479 cases. Children and teenagers (0-19yrs) accounted for 48% of influenza B cases and approximately one third of all influenza cases. Children and teenagers (0-19yrs), young adults (20-44yrs) and middle-aged adults (45-64yrs) accounted for approximately an equal proportion of influenza A(H1N1) cases.

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) Weeks 25-28 (June 19 to July 16, 2016) Cumulative (August 30, 2015 to July 16, 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 due to small values.

Return to first Table 1 - Footnote x referrer

<5 Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 4541 1718 76 2747 1772 6313 19%
5-19 Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 2409 1026 102 1281 2703 5112 15%
20-44 Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 5827 2763 167 2897 2205 8032 24%
45-64 Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 6414 2808 203 3403 1108 7522 22%
65+ Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 4888 1633 452 2803 1612 6500 19%
Total Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 24079 9948 1000 13131 9400 33479 100%
PercentageTable 1 - Footnote 2 Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x Table 1 - Footnote x 72% 41% 4% 55% 28%    

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 between weeks 25 and 28 fluctuated but remained within the same range as the previous report. In week 28, the ILI consultation rate was 23.4 per 1,000 patient visits compared to 13.4 in week 24. In week 28, the highest ILI consultation rate was found in the 0-4 years age group (43.4 per 1,000) and the lowest was found in the ≥65 years of age group (6.7 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 28 for the 2015-16 season: Age 0-4: 43.4; Age 5-19: 33.1; Age 20-64: 22.0; Age 65+: 6.7

Pharmacy Surveillance

In the period of weeks 25-28, the proportion of prescriptions for antivirals continued to decrease steadily to 2.5 antiviral prescriptions per 100,000 total prescriptions in week 28. This rate is lower than the five year historical average for week 28. The proportion of prescriptions for antivirals remains highest among children. In week 28, the proportion reported among children was 8.4 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): 5.3.; Rate wk 28: 2.5

Proportion of antiviral prescriptions by age-group in week 28 for the 2015-16 season: Infant: 0.0; child: 8.3; adult: 2.8; senior: 1.5

Influenza Outbreak Surveillance

In weeks 25-28, no new laboratory confirmed influenza outbreaks were reported. One ILI outbreak was reported in week 25.

To date this season, 428 outbreaks have been reported. At week 28 in the 2014-15 season, 1,732 outbreaks were reported and in the 2013-14 season, 268 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 15 5
13 5 12 4
14 2 14 1
15 1 11 0
16 3 9 1
17 0 7 1
18 0 9 1
19 0 2 0
20 1 1 0
21 0 2 0
22 1 1 0
23 0 0 0
24 0 0 0
25 0 0 0
26 0 0 0
27 0 0 0
28 0 0 0
29 0 0 0
30 0 0 0
31 0 0 0
32 0 0 0
33 0 0 0
34 0 0 0

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In weeks 25-28, three laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). One new ICU admission was reported in week 27.

A total of 225 intensive care unit (ICU) admissions have been reported to date. Children aged 2 to 4 and 5 to 9 years eachaccounted for 27% of ICU admissions . A total of 158 ICU cases (70%) reported at least one underlying condition or comorbidity. Eight influenza-associated deaths have been reported.

To date this season, 1,364 hospitalizations have been reported by the IMPACT network: 903 cases (66%) were due to influenza A and 461 cases (34%) were due to influenza B. This season’s count of pediatric hospitalizations is nearly double that reported up to week 28 in the 2014-15 season (N=713). The total number of cases for the current season also exceeds the total number of cases reported in the past five seasons.

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 16 July 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 124 33 <5 Table 2 - Footnote x 40 164 (12%)
6-23m 282 81 7 194 99 381 (28%)
2-4y 256 80 5 171 117 373 (27%)
5-9y 182 50 <5 Table 2 - Footnote x 146 328 (24%)
10-16y 59 18 <5 Table 2 - Footnote x 59 118 (9%)
Total 903 262 21 620 461 1364 (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 7
52 13 11
1 20 20
2 14 14
3 24 26
4 39 21
5 50 45
6 78 54
7 107 93
8 143 131
9 145 117
10 149 130
11 117 120
12 90 88
13 66 91
14 56 69
15 63 44
16 42 43
17 36 17
18 29 0
19 22 0
20 18 0
21 8 0
22 6 0
23 1 0
24 1 0
25 0 0
26 0 0
27 1 0
28 2 0
29 0 0
30 0 0
31 0 0
32 0 0
33 0 0
34 0 0

Adult Influenza Hospitalizations and Deaths

Surveillance for the 2015-2016 influenza season ended on April 30th, 2016 (week 20).

For the 2015-16 season, 1,153 hospitalizations have been reported by CIRN-SOS (Table 3). The majority of hospitalized cases were due to influenza A (81%) and the largest reported proportion was among adults ≥65 years of age (50%). One hundred and ninety-one intensive care unit (ICU) admissions have been reported of which 132 cases reported at least one underlying condition or comorbidity. A total of 55 deaths have been reported this season with the majority of deaths reported in adults ≥65 years of age (62%).

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 April 30, 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 Table 3 - Footnote x <5 0 <5 <5 Table 3 - Footnote x
20-44 144 50 <5 Table 3 - Footnote x 46 190 (16%)
45-64 331 105 <5 Table 3 - Footnote x 46 377 (33%)
65+ 452 125 24 303 123 575 (50%)
Unknown <5 Table 3 - Footnote x 0 <5 <5 <5
Total 934 285 28 621 219 1153
% 81% 31% 3% 66% 19% 100%

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

Figure 8
Figure 8 - Text Description
Age-group (years) Hospitalizations (n=1149) ICU admissions (n=191) Deaths (n=50)
Table Figure 8 - Footnote x

Suppressed to prevent residual disclosure.

Return to first Table Figure 8 - Fo2tn273x referrer

16-20 0.6% Table Figure 8 - Footnote x% Table Figure 8 - Footnote x%
20-44 16.5% Table Figure 8 - Footnote x% Table Figure 8 - Footnote x%
45-64 32.8% 46.1% 34.5%
65+ 50.0% 34.6% 61.8%

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 28, two hospitalizations were reported by participating provinces and territoriesFootnote *. In total, 33 hospitalizations were reported in weeks 25-28, with the number of cases decreasing each week. No new ICU admissions were reported during the week 25-28 period.

Since the start of the 2015-16 season, 5,350 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 4,151 hospitalizations (78%) were due to influenza A and 1,199 (22%) were due to influenza B. Of the 538 ICU admissions reported, 475 (88%) were due to influenza A. A total of 267 deaths have been reported; all but 42 were associated with influenza A.

Overall this season, hospitalizations have been reported more frequently among adults ≥65 years of age. The largest proportion of ICU admissions was reported in adults 45-64years of age and the highest proportion of fatal cases was reported in adults ≥65 years of age (Figure 9). Pediatric (0-19 years) accounted for 29% of all hospitalizations and 5% of all deaths reported to date this season. Similar to findings from the IMPACT network, there have been more pediatric hospitalizations reported to date compared to the year-end totals in each of the previous four influenza seasons.

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=5350) ICU admissions (n=538) Deaths (n=267)
0-4 18.9% 8.9% 1.9%
5-19 9.7% 6.1% 3.0%
20-44 13.0% 17.8% 7.5%
45-64 26.2% 44.2% 34.5%
65+ 32.2% 22.9% 53.2%

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 2,977 influenza viruses [249 A(H3N2), 1,484 A(H1N1) and 1,244 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 79 A(H3N2) viruses were antigenically characterized as A/Switzerland/9715293/2013-like using antiserum raised against cell-propagated A/Switzerland/9715293/2013.

Sequence analysis was done on 170 A(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): All of the 1,484 A(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 260 influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. A total of 984 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 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 2,103 influenza viruses for resistance to oseltamivir and zanamivir and 1,749 influenza viruses for resistance to amantadine. All but 10 tested viruses were sensitive to oseltamivir. The 10 H1N1 viruses resistant to oseltamivir had a H275Y mutation. All viruses tested for resistance were sensitive to zanamivir. All but two 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) 192 0 (0%) 192 0 (0%) 253 252 (99.6%)
A (H1N1) 1126 10 (0.9%) 1126 0 (0%) 1496 1495 (99.9%)
B 785 0 (0%) 785 0 (0%) NATable 4 - Footnote * NATable 4 - Footnote *
Total 2103 10 (0.5%) 2103 0 (0%) 1749 1747 (99.9%)

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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