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FluWatch report: December 4 to December 10, 2016 (week 49)

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Organization: Public Health Agency of Canada

Date published: 2016-12-16

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Overall Summary

  • Seasonal influenza activity is increasing in Canada, with greater numbers of influenza detections, hospitalizations and outbreaks being reported in week 49.
  • A total of 554 positive influenza detections were reported in week 49. Influenza A(H3N2) continues to be the most common subtype detected.
  • In week 49, 1.1% of visits to sentinel healthcare professionals were due to influenza-like symptoms.
  • Sixteen laboratory-confirmed influenza outbreaks were reported in week 49, with the majority occurring in long-term care facilities.
  • Sentinel hospital networks and participating provinces and territories all reported an increased number of hospitalizations in week 49.
  • For more information on the flu, see our Flu (influenza) web page.

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Influenza/Influenza-like Illness (ILI) Activity (geographic spread)

In week 49, a total of 19 regions in Canada reported no influenza activity. Sporadic influenza activity was reported in 20 regions across 11 provinces and territories (BC, AB, SK, ON, NS, NB, PE, NF, NT, YT and NU). Localized activity was reported in eight regions across four provinces (BC, AB, ON and NS). For more details on a specific region, click on the map. 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 49
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 49, a total of 19 regions in Canada reported no influenza activity. Sporadic influenza activity was reported in 20 regions across 11 provinces and territories (BC, AB, SK, ON, NS, NB, PE, NF, NT, YT and NU). Localized activity was reported in eight regions across four provinces (BC, AB, ON and NS).

Laboratory Confirmed Influenza Detections

The percentage of tests positive for influenza continues to increase with 10.0% of tests positive for influenza in week 49. Compared to the previous influenza A(H3N2)-predominant season in 2014-15, the percent positive (10.0%) was lower than the percent positive reported in week 49 of the 2014-15 season (19.2%). 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 49
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
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
49 157 402 <5 12

Nationally in week 49, there were 554 positive influenza tests. To date, a total of 2,114 laboratory confirmed influenza detections have been reported. Influenza A(H3N2) is the most common subtype detected, representing 77% of detections. 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 49
Figure 3
Figure 3 - Text Description
Reporting
provincesTable Figure 3 - Footnote 1		 Weekly (December 4, 2016 to December 10, 2016) Cumulative (August 28, 2016 to December 10, 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 47 0 36 11 0 333 2 319 12 15 348
AB 235 0 225 10 4 740 5 715 20 18 758
SK 10 0 2 8 0 83 0 18 65 4 87
MB 0 0 0 0 0 13 0 13 0 1 14
ON 129 2 107 20 1 402 10 327 65 19 421
QC 87 0 9 78 5 287 0 43 243 23 310
NB 0 0 0 0 0 10 1 5 4 3 13
NS 5 0 0 5 0 15 0 1 14 0 15
PE 1 0 1 0 0 4 0 4 0 0 4
NL 3 0 3 0 2 17 0 16 1 3 20
YT 22 0 15 7 0 117 0 101 16 1 118
NT 1 0 1 0 0 2 0 2 0 0 2
NU 2 0 2 0 0 3 0 3 0 1 4
Canada 542 2 401 139 12 2026 18 1567 440 88 2114
PercentageTable Figure 3 - Footnote 2 98% 0% 74% 26% 2% 96% 1% 77% 22% 4% 100%

To date this season, detailed information on age and type/subtype has been received for 1,833 laboratory confirmed influenza cases. Adults aged 65+ accounted for over 37% of reported influenza cases. Among cases of influenza A(H3N2), adults aged 65+ accounted for 38% of cases. Compared to the cases reported in the 2014-15 season at week 49, adults aged 65+ account for a smaller proportion of cases this season (approximately 37% in 2016-17 compared to 52% 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
Age groups (years) Weekly (November 27, 2016 to December 10, 2016) Cumulative (August 28, 2016 to December 10, 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 >23 <5 13 10 <5 >126 <5 89 37 19 >145 x%
5-19 65 0 44 21 6 276 0 214 62 12 288 16%
20-44 63 0 49 14 <5 343 5 272 66 16 359 20%
45-64 58 0 36 22 0 344 7 255 82 9 353 19%
65+ 145 0 94 51 <5 >675 <5 517 158 10 >685 x%
Total >354 <5 236 118 11 1767 15 1347 405 66 1833 100%
PercentageTable 1 - Footnote 2 97% x% x% x% 3% 96% 1% 76% 23% 4%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 49, 1.1% of visits to healthcare professionals were due to ILI. The proportion of ILI visits has remained constant for the past three weeks.

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

Number of Sentinels Reporting Week 49: 106

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%

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 49, 16 laboratory confirmed influenza outbreaks were reported: 12 in long-term care (LTC) facilities, one in a hospital and three in institutional or community settings. Of the outbreaks with known strains or subtypes: five outbreaks were due to influenza A of which two were due to influenza A(H3N2) (one in a LTC facility and one in an institutional or community setting) and three were due to influenza A(UnS) (all reported in LTC facilities).

To date this season, 68 outbreaks have been reported and the majority (72%) have occurred in LTC facilities. In comparison at week 49 in the 2014-15 season, the previous influenza A(H3N2)-predominant season, 105 outbreaks were reported, of which 80% occurred in LTC facilities.

Figure 5 - Overall number of new laboratory-confirmed influenza outbreaksFigure 5 - Footnote 1 by report week, Canada, 2016-17, Week 49
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 12 3
50 0 0 0
51 0 0 0
52 0 0 0
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

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 49, 104 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote *. Influenza A accounted for all of the reported hospitalizations, of which 56 (54%) were influenza A(H3N2) and the remainder were influenza A(UnS). Adults aged 65+ accounted for the largest proportion of hospitalizations (65%).

To date this season, 327 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 (238/239) were influenza A(H3N2). Adults 65+ accounted for approximately 62% of the hospitalizations. Ten ICU admissions and less than five deaths have been reported.

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 49
Age Groups (years) Cumulative (August 28, 2016 to December 10, 2016)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 23 <5 >23 (x%) 0  0% 0  0%
5-19 23 <5 >23 (x%) <5 x% <5 x%
20-44 25 <5 >25 (x%) 0  0% 0  0%
45-64 49 <5 >49 (x%) <5 x% 0  0%
65+ 199 <5 >199 (x%) <5 x% <5 x%
Total 319 8 327 (100%) 10  100% 5  100%
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

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

To date this season, 50 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Children aged 0-2 years and 2-4 years, each accounted for 30% of hospitalizations. Influenza A accounted for 84% (n=41) of the reported hospitalizations, of which 48% (n=24) were influenza A(H3N2) and the remainder were A(UnS). Additionally, five intensive care unit (ICU) admissions have been reported, all in children older than 5 years.

Compared to the 2014-15, the previous influenza A(H3N2)-predominant season, there have been approximately half the number of cases reported to date compared to the 2014-15 season, where 95 cases were reported as of week 49.

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 49
Figure 5

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 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 7
6-23 mo 7
2-4 yr 15
5-9 yr 11
10-16 yr 9
Figure 7 - Number of pediatric (≤16 years of age) hospitalizations reported by IMPACT sentinel hospital network, by week, Canada, 2016-17, Week 49
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 #N/A 24 4 47
51 #N/A 35 4 71
52 #N/A 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 week 49, 25 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations were reported by the Canadian Immunization Research Network (CIRN). All cases were due to influenza A and the majority (72%) were in adults aged 65+.

To date this season, greater than 40 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. All hospitalized cases were due to influenza A. Adults aged 65+ accounted for approximately 71% of hospitalizations. To date, less than five ICU admissions and 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 49
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 <5
45-64 yr 10
65+ yr 30
Figure 9 - Percentage of hospitalizations, ICU admissions and deaths with influenza reported by age-group (≥16 year of age), Canada 2015-16, Week 49
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= >40) ICU admissions (n= <5) Deaths (n= <5)
20-44 5.0% - -
45-64 23.8% 50.0% -
65+ 71.4% 50.0% 100.0%
- Supressed due to small values

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 144 influenza viruses [125 A(H3N2), 7 A(H1N1), 12 influenza B]. All influenza A viruses (n=125) and 8 influenza B viruses characterized were antigentically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Four 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 49
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like		 47 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		 78

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 45 influenza A (H3N2) viruses that underwent HI testing, determined that  27 viruses belonged to genetic group 3C.2a and 5 viruses belonged to genetic group 3C.3a. Sequencing is pending for the remaining 13 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.
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)		 8 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)		 4 Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2016-17 Northern Hemisphere quadrivalent influenza vaccine.

Antiviral Resistance

During the 2016-17 season, the National Microbiology Laboratory (NML) has tested 134 influenza viruses for resistance to oseltamivir and zanamivir and 51 influenza viruses for resistance to amantadine. All viruses were sensitive to oseltamivir and zanamivir. All 51 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 49
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 117 0 (0%) 117 0 (0%) 45 45 (100%)
A (H1N1) 6 0 (0%) 6 0 (0%) 6 6 (100%)
B 11 0 (0%) 11 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 134 0 (0%) 134 0 (0%) 51 51 (100%)

Provincial and International Influenza Reports

FluWatch definitions for the 2016-2017 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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