FluWatch report: April 9 – April 15, 2017 (week 15)

Overall Summary

  • Overall, influenza activity continues to decline slowly in Canada.
  • In week 15, influenza B activity surpassed influenza A activity, with 50% or more of influenza laboratory detections, hospitalizations and outbreaks associated with influenza B.
  • In keeping with the predominant circulation of A(H3N2) this season, the majority of laboratory detections, hospitalizations and deaths have been among adults aged 65+ years.
  • For more information on the flu, see our Flu(influenza) web page.

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 15, ten regions across six provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 27 regions across nine provinces and territories. Localized activity was reported in 15 regions across five provinces. One region in QC reported widespread activity in week 15. For more details on a specific region, click on the map.

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Organization:

Date published: 2017-04-21

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 15

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 15, ten regions across six provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 27 regions across nine provinces and territories. Localized activity was reported in 15 regions across five provinces. One region in QC reported widespread activity in week 15.

Laboratory Confirmed Influenza Detections

In week 15, the number (582) and the percentage of tests positive for influenza (12%) decreased slightly from the previous week. The proportion of detections due to influenza B has been steadily increasing since mid-February and reached 50% in week 15. However, the number of influenza B detections remains low compared to the same time period in recent seasons, and declined slightly compared to the previous week. For data on other respiratory virus detections, see the Respiratory Virus Detections in Canada Report on the Public Health Agency of Canada (PHAC) website.

Figure 2 – Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2016-17, week 15

Figure 2

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the start and end of seasonal influenza activity.

Figure 2 - Text Description
Figure 2 - Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, 2016-17
Report Week A(Unsubtyped) A(H3) A(H1)pdm09 Influenza B
35 0 <5 0 0
36 <5 0 <5 9
37 <5 17 0 <5
38 11 28 <5 <5
39 14 41 <5 7
40 0 47 <5 <5
41 10 31 0 <5
42 14 49 <5 6
43 16 76 <5 <5
44 19 110 <5 9
45 31 150 <5 11
46 52 140 <5 7
47 54 200 0 9
48 91 272 <5 7
49 148 414 <5 12
50 305 467 <5 18
51 535 750 <5 17
52 857 1064 <5 33
1 1444 1360 <5 38
2 1516 2118 10 39
3 1354 1412 0 47
4 1336 1220 <5 47
5 1222 1290 7 62
6 1200 1225 9 81
7 1291 1141 11 97
8 1345 899 17 128
9 977 935 7 159
10 802 726 14 203
11 629 347 13 242
12 498 259 <5 302
13 369 221 0 309
14 274 134 6 361
15 223 62 0 292

To date this season, 36,542 laboratory confirmed influenza detections have been reported, of which 93% have been influenza A. Influenza A(H3N2) is the most common subtype detected. For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.

Figure 3 – Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, 2016-17, week 15

Figure 3
Figure 3 - Text Description
Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, 2016-17
Reporting
provincesTable Figure 3 - Footnote 1
Weeks (April 9, 2017 to April 15, 2017) Cumulative (August 28, 2016 to April 15, 2017)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1)pdm09
A
(H3)
ATable Figure 3 - Footnote UnS B
Total
A
Total
A
(H1)pdm09
A
(H3)
ATable Figure 3 - Footnote UnS B
Total
BC 2 0 0 2 22 5310 38 3292 1980 561 5871
AB 15 0 5 10 66 3787 24 3617 146 390 4177
SK 8 0 5 3 16 1742 4 1011 727 162 1904
MB 6 0 4 2 7 467 0 175 292 89 556
ON 51 5 38 8 81 9584 65 7767 1752 662 10246
QC 123 0 0 123 83 10588 0 650 9936 585 11173
NB 55 0 10 45 26 1110 2 119 989 64 1174
NS 17 0 0 17 3 400 0 13 387 22 422
PE 0 0 0 0 1 195 2 193 0 2 197
NL 15 0 0 15 2 431 0 43 388 11 442
YT 0 0 0 0 0 213 0 164 49 9 222
NT 0 0 0 0 1 59 0 58 1 11 70
NU 0 0 0 0 1 85 0 83 2 3 88
Canada 292 5 62 225 309 33971 135 17185 16649 2571 36542
PercentageTable Figure 3 - Footnote 2 49% 2% 21% 77% 51% 93% 0% 51% 49% 7% 100%

To date this season, detailed information on age and type/subtype has been received for 25,251 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for half of the reported influenza cases. Among cases of influenza A(H3N2), adults aged 65+ represented 49% of cases, followed by adults aged 20-64 (32% of cases). Among cases of influenza B, adults aged 20-64 represented 41% of cases.

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, 2016-17, week 15
Age groups (years) Week (April 9, 2017 to April 15, 2017) Cumulative (August 28, 2016 to April 15, 2017)
Influenza A B Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) ATable 1 - Footnote UnS Total A Total A(H1) pdm09 A(H3) ATable 1 - Footnote UnS Total # %
0-4 18 0 0 18 17 2175 13 820 1342 167 2342 9%
5-19 15 0 0 15 23 2178 10 1072 1096 319 2497 10%
20-44 >18 0 <5 18 25 3382 22 1794 1566 313 3695 15%
45-64 >28 0 <5 28 36 3827 19 1932 1876 443 4270 17%
65+ 84 0 9 75 63 11834 10 5372 6452 613 12447 49%
Total 168 0 14 154 164 23396 74 10990 12332 1855 25251 100%
PercentageTable 1 - Footnote 2 51% 0% 8% 92% 49% 93% 0% 47% 53% 7%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 15, 0.9% of visits to healthcare professionals were due to influenza-like illness, a decrease compared to the percentage of visits reported in week 14.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 15

Number of participants reporting in week 15: 107

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
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17
Report week % Visits for ILI
35 0.96%
36 0.96%
37 0.98%
38 0.96%
39 0.94%
40 1.03%
41 2.41%
42 1.04%
43 1.01%
44 1.39%
45 1.32%
46 0.97%
47 1.11%
48 1.07%
49 1.08%
50 1.30%
51 1.73%
52 2.83%
1 1.96%
2 2.22%
3 1.92%
4 2.02%
5 2.31%
6 3.13%
7 1.73%
8 2.19%
9 1.82%
10 1.77%
11 1.70%
12 1.14%
13 1.19%
14 1.33%
15 0.89%

Are you a primary healthcare practitioner (General Practitioner, Nurse Practitioner or Registered Nurse) interested in becoming a FluWatch sentinel?
Please visit our Influenza Sentinel page for more details.

Influenza Outbreak Surveillance

In week 15, 21 laboratory confirmed influenza outbreaks were reported, slightly more compared to the previous week. Of the 14 outbreaks with known strains or subtypes: seven were due to to influenza A and seven to influenza B. One additional outbreak due to ILI was reported in a school.

To date this season, 1,107 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 56 outbreaks (7%) due to influenza B have been reported. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,646 outbreaks were reported, of which 74% occurred in LTC facilities and 81 outbreaks (5%) were due to influenza B.

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, week 15
Figure 5
Figure 5 - Text Description
Figure 5 - Overall number of new laboratory-confirmed influenza outbreaks by report week, Canada, 2016-17
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 0 0
37 0 2 0
38 1 1 1
39 1 3 1
40 0 0 0
41 0 3 0
42 0 3 1
43 0 3 0
44 2 5 2
45 1 1 0
46 2 6 0
47 1 8 0
48 0 2 0
49 1 14 3
50 4 15 4
51 5 32 13
52 7 65 18
1 15 84 22
2 13 83 24
3 19 44 9
4 8 39 8
5 13 36 11
6 4 46 20
7 8 38 8
8 5 39 17
9 4 32 9
10 3 32 9
11 7 22 12
12 2 28 6
13 1 24 8
14 0 11 7
15 1 14 6

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 15, 101 influenza-associated hospitalizations were reported by participating provinces and territories*, a decrease from 146 reported in the previous week. The weekly percentage of influenza B associated hospitalizations has been steadily increasing since week 02, and in week 15, 57% of hospitalizations were associated with influenza B. The largest proportion of hospitalizations was among adults aged 65+ years (66%). Seven intensive care unit (ICU) admissions and three deaths were reported in week 15.

To date this season, 5,891 hospitalizations have been reported, of which 93% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (3064/3088) were influenza A(H3N2). Adults 65+ accounted for 68% of the hospitalizations. A total of 225 ICU admissions and 336 deaths have been reported. The majority of deaths (86%) were reported in adults aged 65+ years.

Table 2 - Cumulative number of hospitalizations, ICU admissions and deaths by age and influenza type reported by participating provinces and territories, Canada 2016-17, week 15
Age Groups (years) Cumulative (August 28, 2016 to April 15, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 435 43 478 (8%) 15  7% <5 Table 2 - Footnote x%
5-19 233 45 278 (5%) 13  6% <5 Table 2 - Footnote x%
20-44 288 18 306 (5%) 20  9% 8  2%
45-64 737 71 808 (14%) 67  30% 35  10%
65+ 3801 220 4021 (68%) 110  49% 289  86%
Total 5494 397 5891 (100%) 225  100% 336  100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 15, 9 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network, which is less than the previous week. Influenza B accounted for half of the cases in week 15. The number of weekly hospitalizations reported since week 05 has been below the six year average for the same time period (Figure 7).

To date this season, 506 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 39% of hospitalizations and influenza A accounted for 86% of the reported hospitalizations. Among the 69 hospitalizations due to influenza B, 33 (48%) were in children over the age of 5 years. In comparison, children over the age of 5 years accounted for 33% of influenza A hospitalizations. Additionally, 85 intensive care unit (ICU) admissions have been reported. Children aged 0-23 months accounted for 27% of ICU cases, and children aged 10-16 years for 29%. A total of 56 ICU cases (72%) reported at least one underlying condition or comorbidity. Less than five deaths have been reported this season.

Figure 6 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2016-17, week 15

Figure 6
Figure 6 - Text Description
Figure 6 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2016-17
Age Group Total
0-5 mo 80
6-23 mo 115
2-4 yr 135
5-9 yr 87
10-16 yr 89

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 15

Figure 7

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2015-16.

The number of hospitalizations reported through IMPACT represents a subset of all influenza-associated pediatric and adult hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

Figure 7 - Text Description
Figure 7 - Number of pediatric (≤16 years of age) hospitalizations reported by IMPACT sentinel hospital network, by week, Canada, 2016-17
Report week 2016-17 Average Min Max
35 0 0 0 0
36 1 0 0 0
37 0 1 0 2
38 0 1 0 2
39 3 0 0 1
40 2 0 0 1
41 0 1 0 2
42 4 1 0 1
43 3 1 0 3
44 6 2 1 4
45 3 3 2 4
46 5 5 1 13
47 3 5 0 9
48 7 10 1 22
49 10 15 2 28
50 19 24 4 47
51 17 35 4 71
52 38 47 7 92
1 48 37 3 75
2 27 36 6 60
3 38 37 2 67
4 34 34 5 47
5 38 39 10 57
6 33 38 15 79
7 28 41 15 118
8 33 48 25 134
9 19 59 12 172
10 17 48 17 114
11 19 45 17 118
12 13 39 14 96
13 14 33 14 57
14 15 27 12 56
15 9 25 14 56
16 #N/A 22 10 41
17 #N/A 18 9 37
18 #N/A 15 6 28
19 #N/A 10 5 18
20 #N/A 9 4 18
21 #N/A 6 2 10
22 #N/A 4 1 7
23 #N/A 2 0 4
24 #N/A 2 0 5
25 #N/A 1 0 3
26 #N/A 1 0 2
27 #N/A 0 0 2
28 #N/A 1 0 1
29 #N/A 0 0 2
30 #N/A 0 0 0
31 #N/A 0 0 0
32 #N/A 0 0 1
33 #N/A 0 0 0
34 #N/A 1 0 2

Adult Influenza Hospitalizations and Deaths

In week 15, 29 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). The proportion of hospitalizations associated with influenza B continues to increase and was 69% in week 15. The majority of cases (79%) occurred in adults aged 65+.

To date this season, 1,453 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 94% of hospitalizations. Adults aged 65+ accounted for 79% of hospitalizations. To date, 103 intensive care unit (ICU) admissions have been reported. A total of 77 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 69 years. Approximately 68 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 85 years.

Figure 8 - Cumulative numbers of adult hospitalizations (≥20 years of age) with influenza by type and age-group reported by CIRN, Canada, 2016-17, week 15

Figure 8
Figure 8 - Text Description
Figure 8 - Cumulative numbers of adult hospitalizations (≥20 years of age) with influenza by type and age-group reported by the CIRN network, Canada, 2016-17
Age Group Total
20-44 yr 89
45-64 yr 221
65+ yr 1143

Figure 9 – Percentage of hospitalizations, ICU admissions and deaths with influenza by age-group (≥20 years of age) reported by CIRN, Canada 2016-17, week 15

Figure 9

The number of hospitalizations reported through CIRN represents a subset of all influenza-associated adult hospitalizations in Canada. Delays in the reporting of data may cause data to change retrospectively.

Figure 9 - Text Description
Figure 9 - Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥20 year of age), CIRN, Canada, 2016-17
Age-group (years) Hospitalizations (n=1453) ICU admissions (n=103) Deaths (n= >62)
- Supressed due to small values
20-44 6.1% 6.8% -
45-64 15.2% 20.4% 4.0%
65+ 78.7% 72.8% 96%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,669 influenza viruses [1431 A(H3N2), 36 A(H1N1), 202 influenza B]. All but one influenza A virus (n=1430) and 46 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. One hundred and fifty-six influenza B viruses were similar to the strain which is only included in the quadrivalent vaccine.

Table 3 – Influenza strain characterizations, Canada, 2016-17, week 15
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
348 Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine.
GeneticallyTable 3 - Footnote 2
A/Hong Kong/4801/2014-like
1082

Viruses belonging to genetic group 3C.2a. A/Hong Kong/4801/2014-like virus belongs to genetic group 3C.2a and is the influenza A(H3N2) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine.

Additionally, genetic characterization of the 348 influenza A (H3N2) viruses that underwent HI testing determined that 287 viruses belonged to genetic group 3C.2a and 61 viruses belonged to genetic group 3C.3a. The majority of viruses belonging to genetic group 3C.3a are inhibited by antisera raised against A/Hong Kong/4801/20143Table 3 - Footnote 3.

Antigenically
A/Indiana/10/2011-likeTable 3 - Footnote 4
1

Viruses antigenically similar to A/Indiana/10/2011, a candidate H3N2v vaccine virus.

Influenza A (H1N1)
A/California/7/2009-like 36 Viruses antigenically similar to A/California/7/2009, the A(H1N1) component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent vaccine influenza vaccine.
Influenza B
B/Brisbane/60/2008-like
(Victoria lineage)
46 Viruses antigenically similar to B/Brisbane/60/2008, the influenza B component of the 2016-17 Northern Hemisphere's trivalent and quadrivalent influenza vaccine
B/Phuket/3073/2013-like
(Yamagata lineage)
156 Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2016-17 Northern Hemisphere quadrivalent influenza vaccine.

During the 2016-17 season, the National Microbiology Laboratory (NML) has tested 932 influenza viruses for resistance to oseltamivir, 884 influenza viruses for resistance to zanamivir and 208 influenza viruses for resistance to amantadine. All but two influenza A(H3N2) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir. All 208 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, week 15
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 717 2 (0.3%) 697 0 (0%) 178 178 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 35 0 (0%) 33 0 (0%) 29 29 (100%)
B 179 0 (0%) 153 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 932 2 (0.2%) 884 0 (0%) 208 208 (100%)

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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