FluWatch report: May 22 to June 18, 2016 (weeks 21-24)

Overall Summary

  • Overall, influenza activity continues to decrease across Canada and has reached interseasonal levels.
  • Sporadic activity is being reported in several parts of Canada; however, the majority of regions are reporting no influenza activity.
  • No influenza outbreaks have been reported since week 22 (beginning of June).
  • Influenza-associated hospitalizations continue to decrease. Ten hospitalizations were reported in week 24
  • 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!

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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Date published: 2016-06-24

Influenza/Influenza-like Illness Activity (geographic spread)

In week 24, influenza activity continues to be reported in parts of Canada. Sporadic activity was reported in 14 regions across six provinces (BC, AB, MB, ON, QC, NB and NU). A total of 34 regions reported no influenza activity.

Figure 1. Map of overall influenza/ILI activity level by province and territory, Canada, week 24

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 24, influenza activity continues to be reported in parts of Canada. Sporadic activity was reported in 14 regions across six provinces (BC, AB, MB, ON, QC, NB and NU). A total of 34 regions reported no influenza activity.

Laboratory Confirmed Influenza Detections

In weeks 21-24, the percentage of tests positive for influenza continued to decrease [from 6.2% in week 21 to 1.1% in week 24]. Compared to the previous five seasons, the percent positive (1.1%) reported in week 24 was within expected levels (confidence interval 1.0-2.6%) and has retuned to 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 21-24, the percentage of tests positive for influenza continued to decrease [from 6.2% in week 21 to 1.1% in week 24].

Nationally in weeks 21-24, there were 389 positive influenza tests reported. Influenza B continues to account for the majority of influenza detections, representing 79% of detections in weeks 21-24. Overall in week 24, laboratory detections of influenza were low across Canada with total of 24 influenza detections reported. To date, 72% of influenza detections have been influenza A and among those subtyped, the vast majority have been influenza A(H1N1) [91% (11019/12147)].

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 21-24 (May 22 to June 18, 2016) Cumulative (August 30, 2015 to June 18, 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 9 <5 <5 5 5 2067 1028 362 677 1168 3155
AB 8 <5 6 <5 13 3962 3638 209 115 1670 5632
SK 0 0 0 0 0 2337 1514 47 776 829 3166
MB <5 <5 0 <5 20 899 186 38 675 240 1139
ON 31 <5 19 Table Figure 3 - Footnote x 85 7686 3266 413 4007 2862 10548
QC 22 <5 0 Table Figure 3 - Footnote x 156 8971 1026 8 7937 3858 12829
NB 7 0 0 7 15 1172 100 5 1067 153 1325
NS 0 0 0 0 0 302 0 <5 Table Figure 3 - Footnote x 11 313
PE <5 <5 0 0 0 66 54 12 Table Figure 3 - Footnote x <5 69
NL 0 0 0 0 0 473 58 <5 Table Figure 3 - Footnote x 28 501
YT 0 0 0 0 0 58 53 <5 <5 19 77
NT <5 0 0 <5 0 122 90 27 5 20 142
NU 0 0 0 0 14 25 6 0 19 34 59
Canada 81 11 26 44 308 28140 11019 1128 15993 10895 39035
Percentage Table Figure 3 - Footnote 2 21% 14% 32% 54% 79% 72% 39% 4% 57% 28% 100%

To date this season, detailed information on age and type/subtype has been received for 33,414 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 21-24 (May 22, 2016 to June 18, 2016) Cumulative (August 30, 2015 to June 18, 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 9 <5 <5 7 60 4533 1714 76 2743 1768 6305 19%
5-19 9 <5 <5 <5 25 2408 1026 101 1281 2695 5105 15%
20-44 14 <5 <5 8 14 5816 2758 166 2892 2197 8017 24%
45-64 <5 0 0 <5 46 6396 2797 201 3398 1103 7505 22%
65+ 15 <5 6 Table 1 - Footnote x 42 4863 1624 446 2793 1610 6482 19%
Total 48 11 12 25 187 24016 9919 990 13107 9373 33414 100%
PercentageTable 1 - Footnote 2 20% 23% 25% 52% 80% 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 decreased from previous weeks from 30.1 per 1,000 patient visits in week 22, to 13.4 per 1,000 patient visits in week 24. The ILI rate for week 21 was lower than expected due to a low response rate resulting from a technical error in data collection. In week 24, the highest ILI consultation rate was found in the 5-19 years age group (30.3 per 1,000) and the lowest was found in the 0-4 years age group (3.6 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 24 for the 2015-16 season:

  • Age 0-4: 3.6;
  • Age 5-19: 30.3
  • Age 20-64: 10.5;
  • Age 65+: 6.2

Pharmacy Surveillance

In the period of weeks 21-24, the proportion of prescriptions for antivirals continued to decrease steadily to 2.9 antiviral prescriptions per 100,000 total prescriptions in week 24. This rate is lower than the five year historical average for week 24. The proportion of prescriptions for antivirals remains highest among children. In week 24, the proportion reported among children was 8.1 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): 9.1.
  • Rate wk 24: 3.0

Proportion of antiviral prescriptions by age-group in week 24 for the 2015-16 season:

  • Infant: 0.0;
  • child: 8.1;
  • adult: 4.1;
  • senior: 1.5

Influenza Outbreak Surveillance

In weeks 21-24, four new laboratory confirmed influenza outbreaks were reported: two in long-term care facilities (LTCF) and two in hospitals. All outbreaks were reported in weeks 21 and 22. Three outbreaks were due to influenza B and one was due to influenza A(unsubtyped).

To date this season, 427 outbreaks have been reported. At week 24 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

Sentinel Pediatric Hospital Influenza Surveillance

Paediatric Influenza Hospitalizations and Deaths

In weeks 21-24, 16 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). The majority of hospitalizations (81%) were due to influenza B.

A total of 222 intensive care unit (ICU) admissions have been reported. Children aged 2 to 4 and 5 to 9 years accounted for 27% and 26% of ICU admissions respectively. A total of 158 ICU cases (71%) 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: 900 cases (66%) were due to influenza A and 464 cases (34%) were due to influenza B. This season's count of pediatric hospitalizations is nearly double that reported up to week 24 in the 2014-15 season (N=711). The current year total number of cases 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 18 June 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 122 33 <5 Table 2 - Footnote x 40 162 (12%)
6-23m 281 80 7 194 99 380 (28%)
2-4y 255 80 5 170 119 374 (27%)
5-9y 183 49 <5 Table 2 - Footnote x 146 329 (24%)
10-16y 59 18 <5 Table 2 - Footnote x 60 119 (9%)
Total 900 260 21 619 464 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
8 142 131
9 146 117
10 149 130
11 117 120
12 89 88
13 67 91
14 58 69
15 66 44
16 40 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

Adult Influenza Hospitalizations and Deaths

Surveillance for the 2015-2016 influenza season ended on April 30th, 2016.

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 (x%)
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 2015-16

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=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 24, 10 hospitalizations were reported by participating provinces and territoriesFootnote *. In total, 98 hospitalizations were reported in weeks 21-24, with the number of cases decreasing each week. Three ICU admissions were reported during the week 21-24 period.

Since the start of the 2015-16 season, 5,267 laboratory-confirmed influenza-associated hospitalizations have been reported. A total of 4,094 hospitalizations (78%) were due to influenza A and 1,173 (22%) were due to influenza B. Of the 537 ICU admissions reported, 474 (88%) were due to influenza A. A total of 264 deaths have been reported; all but 41 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=5267) ICU admissions (n=537) Deaths (n=264)
0-4 18.9% 8.9% 1.9%
5-19 9.7% 6.1% 3.0%
20-44 12.9% 18.1% 7.6%
45-64 26.3% 44.5% 34.8%
65+ 32.1% 22.3% 52.7%

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 2,871 influenza viruses [236 A(H3N2), 1,450 A(H1N1) and 1,185 influenza B].

Influenza A (H3N2): When tested by hemagglutination inhibition (HI) assays, 75 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 161 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 1,450 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 248 influenza B viruses characterized were antigenically similar to the vaccine strain B/Phuket/3073/2013. A total of 937 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 1,966 influenza viruses for resistance to oseltamivir and zanamivir and 1,691 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) 185 0 (0%) 185 0 (0%) 237 236 (99.6%)
A (H1N1) 1092 10 (0.9%) 1092 0 (0%) 1454 1453 (99.9%)
B 689 0 (0%) 689 0 (%) NATable 4 - Footnote * NATable 4 - Footnote *
Total 1966 10 (0.5%) 1966 0 (0%) 1691 1689 (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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