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FluWatch report:  February 19, 2017 to February 25, 2017 (week 8)

Overall Summary

  • Overall, the decline in influenza activity in Canada has been slow compared to previous seasons. Many parts of Canada are still reporting elevated activity in week 08.
  • Widespread or localized influenza activity was reported in 29 regions across 11 provinces.
  • The percentage of tests positive for influenza has remained relatively stable for the past six weeks (ranging from 23% to 25% of tests positive for influenza).
  • In week 08, 57 laboratory confirmed outbreaks were reported (up from 54 reported in the previous week); the majority in long-term care facilities and due to influenza A.
  • In week 08, the number of hospitalizations reported by participating provinces and territories decreased. 
  • A(H3N2) continues to be the most common type of influenza affecting Canadians.
  • The majority of laboratory detections, hospitalizations and deaths have been among adults aged 65+ years.
  • The World Health Organization (WHO) has released the recommended composition of the influenza vaccine for use in the 2017-2018 northern hemisphere influenza season. The recommended strain was changed for the A(H1N1) component. The A(H3N2) and the two B components are unchanged from the current season. 
  • For more information on the flu, see our Flu(influenza) web page.

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Organization:

Public Health Agency of Canada

Date published: 2017-03-03

Related Topics

Influenza/Influenza-like Illness Activity (geographic spread)

In week 08, the YK and two regions in NB reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 19 regions across eight provinces and territories. Localized activity was reported in 28 regions across 11 provinces. Widespread activity was reported in one region in QC. 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 8

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 08, the YK and two regions in NB reported no influenza or influenza-like illness activity. Sporadic influenza activity was reported in 19 regions across eight provinces and territories. Localized activity was reported in 28 regions across 11 provinces. Widespread activity was reported in one region in QC.

Laboratory Confirmed Influenza Detections

In week 08, the number of positive tests (2,337) and the percentage of tests positive for influenza (24%) decreased slightly from the previous week. Peak influenza detections occurred in week 02 at 27%. After a decline from the peak in week 03, detections have remained relatively stable (ranging from 23% to 25% in weeks 03 to 08). 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 8

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 1292 1140 11 97
8 1428 863 14 126

In week 08, the number of positive influenza detections continued to increase in the Atlantic region. In the rest of the country, provinces and territories reported a decrease or a similar number of detections to the previous week.To date, 27,830 laboratory confirmed influenza detections have been reported, of which 98% 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 8

Figure 3
Figure 3 - Text Description
Reporting
provincesTable Figure 3 - Footnote 1		 Weekly (Febuary 19, 2017 to Febuary 25, 2017) Cumulative (August 28, 2016 to Febuary 25, 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 341 5 275 61 47 4080 16 2413 1651 205 4285
AB 76 2 41 33 15 3521 15 3394 112 94 3615
SK 46 0 32 14 0 1484 1 834 649 19 1503
MB 57 0 13 44 7 277 0 103 174 23 300
ON 483 7 375 101 25 8196 45 6603 1548 145 8341
QC 998 0 60 938 30 8100 0 572 7526 191 8291
NB 127 0 16 111 0 599 2 85 512 4 603
NS 30 0 0 30 0 240 0 13 227 2 242
PE 13 0 13 0 0 150 2 148 0 1 151
NL 65 0 0 65 0 177 0 43 134 5 182
YT 6 0 5 1 0 203 0 155 48 2 205
NT 4 0 3 1 2 45 0 44 1 3 48
NU 5 0 2 3 0 63 0 59 4 1 64
Canada 2251 14 835 1402 126 27135 81 14466 12586 695 27830
PercentageTable Figure 3 - Footnote 2 95% 1% 37% 62% 5% 98% 0% 53% 46% 2% 100%

To date, detailed information on age and type/subtype has been received for 19,666 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for almost half of the reported influenza cases. Among cases of influenza A(H3N2), adults aged 65+ represented 48% of cases, followed by adults aged 20-64 (34% of cases). In the previous influenza A(H3N2)-predominant season in 2014-15, adults aged 65+ represented 61% of cases and adults aged 20-64 represented 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 8
Age groups (years) Weekly (February 19 to February 25, 2017) Cumulative (August 28, 2016 to February 25, 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 >151 <5 18 133 5 1716 7 687 1022 63 1779 9%
5-19 116 0 19 97 6 1867 6 923 938 84 1951 10%
20-44 >156 <5 22 134 13 2880 18 1556 1306 87 2967 15%
45-64 210 0 33 177 17 3160 16 1640 1504 111 3271 17%
65+ >703 <5 106 597 31 9540 9 4462 5069 158 9698 49%
Total >1336 <5 198 1,138 72 19163 56 9268 9839 503 19666 100%
PercentageTable 1 - Footnote 2 95% 0% 15% 85% 5% 97% 0% 48% 51% 3%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 08, 2.5% of visits to healthcare professionals were due to influenza-like illness, up from 1.7% in the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 8

Number of Sentinels Reporting Week 08: 101

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 2.49%

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 08, 57 laboratory confirmed influenza outbreaks were reported (four more than the previous week). Among the reported outbreaks: 35 were in long-term care (LTC) facilities, five in hospitals and 17 in institutional or community (other) settings. Of the outbreaks with known strains or subtypes, 14 were due to influenza A(H3N2), 23 were due to influenza A(UnS), two were due to influenza B and one outbreak was due to influenza A(H3N2) and B. An additional outbreak due to ILI was reported in a school.

To date this season, 855 outbreaks have been reported and the majority (67%) have occurred in LTC facilities. Compared to the same period in the most recent previous A(H3N2) predominant season (2014-15), 1,398 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 8
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 47 20
7 8 38 8
8 5 35 17

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 08, 245 influenza-associated hospitalizations were reported by participating provinces and territories, down slightly from  250 reported in the previous week*. Influenza A accounted for nearly all of hospitalizations (95%). The largest proportion of hospitalizations were among adults aged 65+ (70%). A total of less than five intensive care unit (ICU) admissions and 19 deaths were reported in week 08.

To date this season, 4,296 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 (2388/2399) were influenza A(H3N2). Adults 65+ accounted for 69% of the hospitalizations. A total of 149 ICU admissions and greater than 181 deaths have been reported. The majority of deaths 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 8
Age Groups (years) Cumulative (August 28, 2016 to Feb. 25 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 314 12 326 (8%) 9 6% <5 x%
5-19 180 12 192 (4%) 12 8% <5 x%
20-44 225 5 230 (5%) 13 9% 0 x%
45-64 580 13 593 (14%) 43 30% 28 15%
65+ 2916 38 2954 (69%) 72 50% 154 84%
Total 4151 70 4295 (100%) 144 103% >181 100%
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

In week 08, 19 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. All but two cases were due to influenza A. The number of hospitalizations reported in week 08 is below the six year average for the same time period (Figure 7).

To date this season, 393 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 40% of hospitalizations. Influenza A accounted for 93% (n=361) of the reported hospitalizations, of which 40% (n=137) were influenza A(H3N2) and the remainder were A(UnS). Additionally, 65 intensive care unit (ICU) admissions have been reported, of which the largest proportion (30%) was reported in children 0-23 months. A total of 42 ICU cases reported at least one underlying condition or comorbidity. Less than five deaths have been reported this season.

In 2014-15, the previous influenza A(H3N2)-predominant season, there were 541 hospitalizations, 66 ICU admissions and less than five deaths reported as of week 08.

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 8

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 67
6-23 mo 85
2-4 yr 105
5-9 yr 64
10-16 yr 68

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 8

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 20 24 4 47
51 17 35 4 71
52 38 47 7 92
1 48 37 3 75
2 28 36 6 60
3 38 37 2 67
4 43 34 5 47
5 28 39 10 57
6 34 38 15 79
7 28 41 15 118
8 19 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 06, 72 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 of cases (78%) occurred in adults aged 65+.

To date this season, 829 laboratory-confirmed influenza-associated adult (≥20 years of age) hospitalizations have been reported by CIRN. All but eight hospitalized cases were due to influenza A. Adults aged 65+ accounted for 77% of hospitalizations. To date, approximately 41 intensive care unit (ICU) admissions have been reported. A total of 29 ICU cases reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 67 years. Approximately 26 deaths have been reported this season, the majority in adults aged 65+. The median age of reported deaths was 84 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 8

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 73
45-64 yr 158
65+ yr 812

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 8

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
Age-group (years) Hospitalizations (n = 1043) ICU admissions (n = 57) Deaths (n ≥36)
20-44 7.0% 8.8% 0.0%
45-64 15.1% 21.1% 5.0%
65+ 77.9% 70.2% 94.7%
- Supressed due to small values

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 972 influenza viruses [888 A(H3N2), 20 A(H1N1), 64 influenza B].  All but one influenza A virus (n=887) and 27 influenza B viruses characterized were antigentically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Thirty-seven influenza B viruses were similar to the strain which is only included in the quadrivalent vaccine.

The World Health Organization (WHO) has released the recommended composition of the influenza vaccine for use in the 2017-2018 northern hemisphere influenza season. Trivalent vaccines are recommended to contain: 1) an A/Michigan/45/2015 (H1N1)pdm09-like virus; 2) an A/Hong Kong/4801/2014 (H3N2)-like virus; and 3) a B/Brisbane/60/2008-like virus (Victoria lineage). Quadrivalent vaccines are recommended to contain the above three viruses and a B/Phuket/3073/2013-like virus (Yamagata lineage).

Table 3 – Influenza strain characterizations, Canada, 2016-17, week 8
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like		 265 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		 622

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 265 influenza A (H3N2) viruses that underwent HI testing determined that 224 viruses belonged to genetic group 3C. 2a and 38 viruses belonged to genetic group 3C.3a. Sequencing is pending for the remaining 3 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 20 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)		 27 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)		 37 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 562 influenza viruses for resistance to oseltamivir and zanamivir and 158 influenza viruses for resistance to amantadine. All viruses were sensitive to oseltamivir and zanamivir. All 158 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, week 8
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 489 0 (0%) 489 0 (0%) 140 140 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 18 0 (0%) 18 0 (0%) 17 17 (100%)
B 54 0 (0%) 54 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 562 0 (0%) 562 0 (0%) 158 158 (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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