FluWatch report: April 16 – April 22, 2017 (week 16)

Overall Summary

  • Overall, influenza activity continues to decline slowly in Canada.
  • In week 16, influenza B activity continued to exceed 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 16, eight regions across six provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 32 regions across 11 provinces and territories. Localized activity was reported in 13 regions across six provinces. For more details on a specific region, click on the map. 

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Organization:

Date published: 2017-04-28

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 16

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 16, eight regions across six provinces and territories reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 32 regions across 11 provinces and territories. Localized activity was reported in 13 regions across six provinces.

Laboratory Confirmed Influenza Detections

In week 16, the number of tests positive for influenza (568) declined slightly compared to the previous week. The percentage of tests positive (11.6%) was similar to the previous week with an increasing proportion of influenza B (60% in week 16). However, the number of influenza B detections remains low compared to the same time period in recent seasons. 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 16

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
14 273 134 6 365
15 219 72 0 321
16 162 58 9 339
17 0 0 0 0
18 0 0 0 0
19 0 0 0 0
20 0 0 0 0
21 0 0 0 0
22 0 0 0 0
23 0 0 0 0
24 0 0 0 0
25 0 0 0 0
26 0 0 0 0
27 0 0 0 0
28 0 0 0 0
29 0 0 0 0
30 0 0 0 0
31 0 0 0 0
32 0 0 0 0
33 0 0 0 0
34 0 0 0 0

To date this season, 37,152 laboratory confirmed influenza detections have been reported, of which 92% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season. 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 16

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
Weekly (April 16, 2017 to April 22, 2017) Cumulative (August 28, 2016 to April 22, 2016)
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 13 1 9 3 41 5318 42 3294 1982 613 5931
AB 23 0 7 16 59 3791 24 3628 139 448 4239
SK 0 0 0 0 19 1749 4 1013 732 193 1942
MB 21 0 14 7 15 470 0 176 294 92 562
ON 104 5 77 22 111 9642 69 7812 1761 783 10425
QC 163 0 0 163 76 10700 0 650 10048 659 11359
NB 26 0 0 26 15 1138 3 126 1009 85 1223
NS 14 0 0 14 5 409 0 13 396 25 434
PE 3 0 3 0 0 195 2 193 0 2 197
NL 32 0 0 32 2 440 0 43 397 14 454
YT 1 0 1 0 0 213 0 164 49 12 225
NT 1 0 1 0 0 59 0 58 1 13 72
NU 0 0 0 0 1 85 0 83 2 4 89
Canada 401 6 112 283 344 34209 144 17253 16810 2943 37152
PercentageTable Figure 3 - Footnote 2 54% 1% 28% 71% 46% 92% 0% 50% 49% 8% 100%

To date this season, detailed information on age and type/subtype has been received for 25,526 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. Cases of influenza A(H3N2) were reported predominantly among adults aged 65+ (49% of cases), followed by adults aged 20-64 (34%) and children 0-19 years (17%). Cases of influenza B have been distributed more evenly across age-groups, with adults aged 65+ representing 33% of cases, adults aged 20-64 41% of cases, and children aged 0-19 years 26% 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 16
Age groups (years) Weekly (April 16 to April 22, 2017) Cumulative (August 28, 2016 to April 22, 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 # %
<5 12 0 0 12 11 2187 13 820 1354 178 2365 9%
5-19 5 0 0 5 23 2183 10 1072 1101 342 2525 10%
20-44 17 0 0 17 35 3399 22 1794 1583 348 3747 15%
45-64 >25 0 <5 25 42 3853 19 1933 1901 485 4338 17%
65+ >50 0 <5 50 50 11888 10 5376 6502 663 12551 49%
Total 114 0 5 109 161 23510 74 10995 12441 2016 25526 100%
PercentageTable 1 - Footnote 2 41% 0% 4% 96% 59% 92% 0% 47% 53% 8%

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 16, 1.0% of visits to healthcare professionals were due to influenza-like illness, an increase compared to the percentage of visits reported in week 15.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 16

Number of Sentinels Reporting Week 16: 104

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 0.88%
16 1.00%
17  
18  
19  
20  
21  
22  
23  
24  
25  
26  
27  
28  
29  
30  
31  
32  
33  
34  

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 16, 11 laboratory-confirmed influenza outbreaks were reported, fewer than in the previous week. Of the four outbreaks with known strains or subtypes: two were due to influenza A and two were due to influenza B. One additional outbreak due to ILI was reported in a school daycare.

To date this season, 1,119 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 59 outbreaks (8%) due to influenza B have been reported. During the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,671 outbreaks were reported, of which 74% occurred in LTC facilities. 

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, week 16
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
16 2 8 1
17 0 0 0
18 0 0 0
19 0 0 0
20 0 0 0
21 0 0 0
22 0 0 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

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 16, 121 influenza-associated hospitalizations were reported by participating provinces and territories*, an increase from 101 reported in the previous week. The weekly percentage of influenza B associated hospitalizations has been increasing since week 02, although the proportion declined slightly to 50% of hospitalizations in week 16 compared to 57% in week 15. The largest proportion of hospitalizations was among adults aged 65+ years (69%). Seven intensive care unit (ICU) admissions and 15 deaths were reported in week 16.

To date this season, 6,026 hospitalizations have been reported, of which 92% were due to influenza A. Among cases for which the subtype of influenza A was reported, 99% were influenza A(H3N2). Adults 65+ accounted for 68% of the hospitalizations. A total of 236 ICU admissions and 346 deaths have been reported. The majority of deaths (88%) 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 16
Age Groups (years) Cumulative (August 28, 2016 to April 22, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 436 50 486 (8%) 15  6% <5 Table 2 - Footnote x%
5-19 234 51 285 (5%) 15  6% <5 Table 2 - Footnote x%
20-44 289 24 313 (5%) 23  10% 5  1%
45-64 743 84 827 (14%) 70  30% 34  10%
65+ 3857 258 4115 (68%) 113  48% 304  88%
Total 5559 467 6026 (100%) 236  100% 346  100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In week 16, 11 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network, of which 7 were associated with influenza B. In keeping with influenza activity this season, pediatric hospitalizations have been declining since the peak in early January, and the proportion of cases due to influenza B has increased in March and April. The number of weekly hospitalizations has been below the six year average since early February (Figure 7).

To date this season, 524 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 38% of hospitalizations and influenza A accounted for 85%  of the reported hospitalizations. Among the 79 hospitalizations due to influenza B, 40 (51%) 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, 87 intensive care unit (ICU) admissions have been reported. Children aged 0-23 months accounted for 26% of ICU cases, and children aged 10-16 years for 30%. A total of 60 ICU cases (70%) 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 16

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 81
6-23 mo 119
2-4 yr 137
5-9 yr 97
10-16 yr 90

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

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 26 36 6 60
3 39 37 2 67
4 34 34 5 47
5 38 39 10 57
6 33 38 15 79
7 29 41 15 118
8 33 48 25 134
9 20 59 12 172
10 17 48 17 114
11 19 45 17 118
12 13 39 14 96
13 14 33 14 57
14 14 27 12 56
15 15 25 14 56
16 11 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 16, 16 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN), half as many as in the week before. The proportion of hospitalizations associated with influenza B continues to increase and was 81% in week 16. The majority of cases (69%) occurred in adults aged 65+.

To date this season, 1,505 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. Influenza A accounted for 92% of hospitalizations. Adults aged 65+ accounted for 78% of hospitalizations. To date, 113 intensive care unit (ICU) admissions have been reported. Among cases with available data, 85 ICU cases (91%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 69 years. Approximately 70 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 16

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 90
45-64 yr 229
65+ yr 1162

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 16

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= 1481) ICU admissions (n= 110) Deaths (n= 69)
- Supressed due to small values
20-44 6.1% 6.4% -
45-64 15.5% 20.0% -
65+ 78.5% 73.6% >93%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 1,723 influenza viruses [1466 A(H3N2), 36 A(H1N1), 221 influenza B].  All but one influenza A virus (n=1465) and 52 influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. One hundred and sixty-nine 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 16
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
350 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
1115

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 350 influenza A (H3N2) viruses that underwent HI testing determined that 288 viruses belonged to genetic group 3C.2a and 62 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/4801/2014Table 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 influenza vaccine.
Influenza B
B/Brisbane/60/2008-like
(Victoria lineage)
52 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)
169 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 971 influenza viruses for resistance to oseltamivir, 970 influenza viruses for resistance to zanamivir and 213 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 213 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 16
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 721 2 (0.3%) 720 0 (0%) 183 183 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 35 0 (0%) 34 0 (0%) 29 29 (100%)
B 214 0 (0%) 215 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 971 2 (0.2%) 970 0 (0%) 213 213 (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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