FluWatch report: December 18 to December 31, 2016 (weeks 51 and 52)

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Organization: Public Health Agency of Canada

Date published: 2017-01-06

  • Seasonal influenza activity continues to increase in Canada, with greater numbers of influenza detections, hospitalizations and outbreaks being reported in weeks 51 and 52.
  • A total of 1,948 positive influenza detections were reported in week 52. Influenza A(H3N2) continues to be the most common subtype detected.
  • Seventy-one laboratory-confirmed influenza outbreaks were reported in week 52, with the majority occurring in long-term care facilities.
  • Adults aged 65+ years accounted for the largest proportion of hospitalizations and deaths reported from adult sentinel networks and participating Provinces and Territories.
  • Influenza activity started early this season, but so far activity has been lower than the 2014-15 season when A(H3N2) was the predominant subtype.
  • For more information on the flu, see our Flu (influenza) web page.

In week 52, a total of 18 regions in Canada reported no influenza activity. Sporadic influenza activity was reported in 19 regions across all provinces and territories except QC and SK. Localized activity was reported in 13 regions across four provinces (ON, SK, AB and BC). Widespread activity was reported in three regions (one each in SK, AB and BC). For more details on a specific region, click on the map.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, Week 52
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 52, a total of 18 regions in Canada reported no influenza activity. Sporadic influenza activity was reported in 19 regions across all provinces and territories except QC and SK. Localized activity was reported in 13 regions across four provinces (ON, SK, AB and BC). Widespread activity was reported in three regions (one each in SK, AB and BC).

The percentage of tests positive for influenza increased from 16% in week 51 to 24% in week 52. Compared to the previous influenza A(H3N2)-predominant season in 2014-15, the percent positive in week 52 (24%) was lower than the percent positive reported in week 52 of the 2014-15 season (34%). 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, Weeks 51 & 52
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
51 536 749 <5 17
52 1027 1018 <5 27
1 0 0 0 0
2 0 0 0 0
3 0 0 0 0
4 0 0 0 0
5 0 0 0 0
6 0 0 0 0
7 0 0 0 0
8 0 0 0 0
9 0 0 0 0
10 0 0 0 0
11 0 0 0 0
12 0 0 0 0
13 0 0 0 0
14 0 0 0 0
15 0 0 0 0
16 0 0 0 0
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

Nationally in week 52, 1,948 positive influenza tests were reported, up from 1,229 tests reported in week 51. To date, a total of 6,180 laboratory confirmed influenza detections have been reported. Influenza A(H3N2) is the most common subtype detected, representing 99% of subtyped influenza A detections (3812/3835). 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 52
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 (December 18, 2016 to December 31, 2016) Cumulative (August 28, 2016 to December 31, 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 406 0 264 142 4 810 2 620 188 20 830
AB 680 1 635 44 3 1671 6 1603 62 24 1695
SK 180 0 95 85 2 373 0 153 220 7 380
MB 3 0 3 0 6 17 0 17 0 7 24
ON 962 2 700 260 10 1556 13 1163 380 33 1589
QC 910 0 25 885 19 1343 0 78 1264 52 1395
NB 13 0 3 10 0 25 1 9 15 3 28
NS 6 0 0 6 0 27 0 1 26 0 27
PE 2 0 2 0 0 8 0 8 0 0 8
NL 2 0 0 2 1 22 0 16 6 4 26
YT 25 0 17 8 0 164 0 132 32 1 165
NT 3 0 3 0 0 6 0 6 0 0 6
NU 0 0 0 0 0 6 0 6 0 1 7
Canada 3192 3 1747 1442 45 6028 22 3812 2193 152 6180
PercentageTable Figure 3 - Footnote 2 99% 0% 55% 45% 1% 98% 0% 63% 36% 2% 100%

To date this season, detailed information on age and type/subtype has been received for 5,008 laboratory confirmed influenza cases. Adults aged 65+ were the age group that accounted for the largest proportion of reported influenza cases (>45%) and the largest proportion of influenza A (H3N2) cases. Compared to the cases reported in the 2014-15 season at week 52, adults aged 65+ account for a smaller proportion of cases this season (approximately 45% in 2016-17 compared to 62% in 2014-15). Adults aged 45-64 account for a greater proportion of cases this season (approximately 23% in 2016-17 compared to 12% in 2014-15).

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, 2016-17, Week 52
Age groups (years) Weekly (December 11, 2016 to December 31, 2016) Cumulative (August 28, 2016 to December 31, 2016)
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 # %
<5 190 0 92 98 6 >359 <5 207 152 28 >387 x%
5-19 228 0 124 104 <5 >594 <5 430 164 21 >615 x%
20-44 325 0 190 135 <5 782 5 568 209 21 803 16%
45-64 >525 <5 273 252 9 1,147 8 678 461 19 1,166 23%
65+ >1,056 <5 493 563 7 >2,011 <5 1207 804 20 >2,031 x%
Total 2,327 <5 1,172 1,152 27 4,899 19 3,090 1,790 109 5,008 100%
PercentageTable 1 - Footnote 2 99% 0% 50% 50% 1% 98% 0% 63% 37% 2%

Healthcare Professionals Sentinel Syndromic Surveillance

In week 52, 3.4% of visits to healthcare professionals were due to ILI, up from week 51 where 2.0% of visits were due to ILI.

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

Number of Sentinels Reporting Week 52: 60

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 1.09%
50 1.33%
51 2.02%
52 3.40%

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.

In week 52, 71 laboratory confirmed influenza outbreaks were reported: 49 in long-term care (LTC) facilities, five in hospitals and 17 in institutional or community settings. Of the outbreaks with known strains or subtypes: 57 outbreaks were due to influenza A of which 17 were due to influenza A(H3N2) (15 in LTC facilities and two in institutional or community settings), 40 were due to influenza A(UnS) (24 in LTC facilities, three in hospitals and 13 in institutional or community settings) and one was due to influenza B (in a LTC facility).

To date this season, 206 outbreaks have been reported and the majority (67%) have occurred in LTC facilities. In comparison at week 52 in the 2014-15 season, the previous influenza A(H3N2)-predominant season, 457 outbreaks were reported, of which 76% occurred in LTC facilities.

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, Week 52
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 3
51 5 24 13
52 5 49 17
1 0 0 0
2 0 0 0
3 0 0 0
4 0 0 0
5 0 0 0
6 0 0 0
7 0 0 0
8 0 0 0
9 0 0 0
10 0 0 0
11 0 0 0
12 0 0 0
13 0 0 0
14 0 0 0
15 0 0 0
16 0 0 0
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

In week 52, 185 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote *. Influenza A accounted for all but two of the reported hospitalizations. Adults aged 65+ accounted for the largest proportion of hospitalizations (72%).

To date this season, 892 hospitalizations have been reported, of which 98% were due to influenza A. Among cases for which the subtype of influenza A was reported, almost all (576/578) were influenza A(H3N2). Adults 65+ accounted for approximately 66% of the hospitalizations. Thirty-two intensive care unit (ICU) admissions and 20 deaths have been reported. The majority of deaths (80%) 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 52
Age Groups (years) Cumulative (August 28, 2016 to December 31, 2016)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
Note: Influenza-associated hospitalizations are not reported to PHAC by: BC, NU, and QC. Only hospitalizations that require intensive medical care are reported by SK. ICU admissions
x Supressed to prevent residual disclosure
0-4 53 <5 >53 (x%) <5 x% 0  0%
5-19 56 <5 >56 (x%) <5 x% <5 x%
20-44 57 <5 >57 (x%) <5 x% 0  0%
45-64 126 <5 >126 (x%) 9  28% <5 x%
65+ 585 7 592 (66%) 16  50% 16  80%
Total 877 15 892 (100%) 32  100% 20  100%

Pediatric Influenza Hospitalizations and Deaths

In weeks 51 and 52, a total 48 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All but one case was due to influenza A. The number of hospitalizations reported in week 51 and 52 were below the six-year average number of hospitalizations for those weeks.

To date this season, 117 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-2 years accounted for approximately 36% of hospitalizations. Influenza A accounted for 89% (n=104) of the reported hospitalizations, of which 53% (n=55) were influenza A(H3N2) and the remainder were A(UnS). Additionally, 18 intensive care unit (ICU) admissions have been reported, of which 67% were reported in children aged five years and older. No deaths have been reported this season.

Compared to 2014-15, the previous influenza A(H3N2)-predominant season, where 262 hospitalizations were reported as of week 52, there has been approximately half the number of cases reported to date in the current 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 52
Figure 5
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 21
6-23 mo 20
2-4 yr 28
5-9 yr 23
10-16 yr 24
Figure 7 - Number of pediatric (≤16 years of age) hospitalizations reported by IMPACT sentinel hospital network, by week, Canada, 2016-17, Weeks 51 & 52
Figure 5

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 4 1 0 3
44 5 2 1 4
45 3 3 2 4
46 8 5 1 13
47 1 5 0 9
48 7 10 1 22
49 10 15 2 28
50 20 24 4 47
51 18 35 4 71
52 30 47 7 92
1 #N/A 37 3 75
2 #N/A 36 6 60
3 #N/A 37 2 67
4 #N/A 34 5 47
5 #N/A 39 10 57
6 #N/A 38 15 79
7 #N/A 41 15 118
8 #N/A 48 25 134
9 #N/A 59 12 172
10 #N/A 48 17 114
11 #N/A 45 17 118
12 #N/A 39 14 96
13 #N/A 33 14 57
14 #N/A 27 12 56
15 #N/A 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 weeks 51 and 52, a total of 151 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). All but two cases were due to influenza A and the greatest proportion of cases (67%) occurred in adults aged 65+.

To date this season, 209 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. All but two hospitalized cases were due to influenza A. Adults aged 65+ accounted for approximately 68% of hospitalizations. To date, greater than nine ICU admissions and less than five deaths have been reported.

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, Week 52
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 13
45-64 yr 50
65+ yr 143
Figure 9 - Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥16 year of age), Canada 2015-16, Week 52
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= >206) ICU admissions (n= <9) Deaths (n= <5)
- Supressed due to small values
20-44 6.3% 15.0% 0.0%
45-64 24.3% 15.0% 0.0%
65+ 69.4% 69.2% 100.0%

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 199 influenza viruses [175 A(H3N2), 7 A(H1N1), 17 influenza B]. All but one influenza A virus (n=174) and 9 influenza B viruses characterized were antigentically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Eight influenza B viruses were similar to the strain which is included only in the quadirvalent vaccine.

Table 3 - Influenza strain characterizations, Canada, 2016-17, Week 52
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like
62 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
112

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 62 influenza A (H3N2) viruses that underwent HI testing determined that 48 viruses belonged to genetic group 3C.2a and 10 viruses belonged to genetic group 3C.3a. Sequencing is pending for the remaining four isolates.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 7 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)
9 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)
8 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 182 influenza viruses for resistance to oseltamivir and zanamivir and 89 influenza viruses for resistance to amantadine. All viruses were sensitive to oseltamivir and zanamivir. All 89 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 52
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 159 0 (0%) 159 0 (0%) 82 82 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 6 0 (0%) 6 0 (0%) 6 6 (100%)
B 16 0 (0%) 16 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 182 0 (0%) 182 0 (0%) 89 89 (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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