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FluWatch report: May 21 – June 17, 2017 (weeks 21-24)

Overall Summary

  • Influenza activity has crossed the seasonal threshold indicating the end of the 2016-17 influenza season, although regions across the country continue to report low-level circulation of influenza.
  • In weeks 21-24, influenza B continued to be the predominant circulating influenza virus in Canada. The majority of influenza B viruses characterized this season are similar to the strain included only in the quadrivalent influenza vaccine for 2016-17. 
  • FluWatch will publish monthly reports over the summer. The next report will be published on July 28, 2017. We continue to monitor influenza and other respiratory infections  via the RVDSS report, published every Thursday.
  • For more information on the flu, see our Flu(influenza) web page.

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Influenza/Influenza-like Illness Activity (geographic spread)

In weeks 21-24, influenza or influenza-like illness activity levels continued to decline with an increasing number of regions reporting no activity. In week 24, three regions in three provinces reported localized activity, and 17 regions across seven provinces and territories reported sporadic activity. For more details on a specific region, click on the map. 

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Public Health Agency of Canada

Date published: 2017-06-23

Related Topics

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, Week 24

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 24, three regions in three provinces reported localized activity, and 17 regions across seven provinces and territories reported sporadic activity.

Laboratory Confirmed Influenza Detections

In weeks 21-24, the number of tests positive for influenza continued to decrease, and the percentage of tests positive declined from 6% in week 21 to 2%  in week 24, crossing the seasonal threshold of 5%. This indicates the end of the 2016-17 influenza season in Canada. Influenza B remained the most common type of influenza detected in weeks 21-24, representing between 75-85% of weekly detections during this period. 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 24

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
15 216 73 0 321
16 167 59 9 347
17 113 38 <5 316
18 64 47 0 283
19 36 30 0 259
20 13 26 <5 228
21 13 12 0 168
22 9 14 7 94
23 13 8 <5 75
24 0 <5 <5 47

To date this season, 39,047 laboratory-confirmed influenza detections have been reported, of which 89% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing over 99% of influenza A 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 24

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 (May 21, 2017 to June 17, 2017) Cumulative (August 28, 2016 to June 17, 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 16 1 13 2 46 5344 44 3310 1990 713 6057
AB 17 5 11 1 139 3819 30 3648 141 738 4557
SK 8 0 3 5 40 1788 4 1044 740 352 2140
MB 0 0 0 0 16 484 1 189 294 133 617
ON 41 5 23 13 166 9781 78 7909 1794 1195 10976
QC 20 0 0 20 108 10874 0 650 10222 972 11846
NB 4 0 1 3 24 1164 3 131 1030 156 1320
NS 1 0 0 1 3 417 0 13 404 33 450
PE 0 0 0 0 1 196 2 194 0 5 201
NL 1 0 0 1 31 447 0 43 404 59 506
YT 1 0 0 1 3 167 0 165 2 24 191
NT 0 0 0 0 3 59 0 58 1 23 82
NU 0 0 0 0 13 85 0 83 2 19 104
Canada 109 11 51 47 593 34625 162 17437 17024 4422 39047
PercentageTable Figure 3 - Footnote 2 16% 10% 47% 43% 84% 89% 0% 50% 49% 11% 100%

To date this season, detailed information on age and type/subtype has been received for 26,897 laboratory-confirmed influenza cases (Table 1). Among cases with reported age and type/subtype information, adults aged 65+ accounted for nearly half of the reported influenza cases. Adults aged 65+ have predominantly been affected by influenza A accounting for 51% of influenza A detections. Influenza B, while much smaller in number, is mainly affecting individuals less than 65 years of age. 

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 24
Age groups (years) Weeks (May 21, 2017 to June  17, 2017) Cumulative (August 28, 2016 to June 17, 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 <5 0 <5 <5 17 2249 20 832 1397 259 2508 9%
5-19 <5 0 <5 <5 46 2219 18 1078 1123 486 2705 10%
20-44 <5 0 <5 <5 23 3442 36 1803 1603 496 3938 15%
45-64 24 5 13 6 39 3941 31 1967 1943 648 4589 17%
65+ 18 <5 10 6 72 12109 24 5450 6635 1048 13157 49%
Total >45 >5 26 19 197 23960 129 11130 12701 2937 26897 100%
PercentageTable 1 - Footnote 2 21% 13% 50% 37% 79% 89% 1% 46% 53% 11%    

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 24, 0.4% of visits to healthcare professionals were due to influenza-like illness.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2016-17, week 24

Number of Sentinels Reporting Week 24: 93

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 1.13%
13 1.18%
14 1.31%
15 0.88%
16 0.98%
17 0.86%
18 0.81%
19 0.96%
20 0.85%
21 0.94%
22 0.64%
23 0.90%
24 0.44%

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

During the period of weeks 21-24, 14 laboratory-confirmed influenza outbreaks were reported, of which 8 were in long-term care facilities, three were in hospitals, and three were in other settings.

To date this season, 1,190 outbreaks have been reported and the majority (66%) have occurred in LTC facilities. A total of 87 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), 1,732 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 24
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 12 6
18 1 6 6
19 2 10 3
20 0 6 3
21 0 4 1
22 2 2 0
23 1 1 2
24 0 1 0

Provincial/Territorial Influenza Hospitalizations and Deaths

During the period of weeks 21-24, the number of weekly influenza-associated hospitalizations reported by participating provinces and territories* fell by more than half. In week 24, 20 hospitalizations were reported, of which 12 were associated with influenza B and 55% occurred in adults 65+. Nine intensive care unit (ICU) admissions and 13 deaths were reported between weeks 21-24.

To date this season, 6,486 hospitalizations have been reported, of which 87% 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 67% of the hospitalizations. A total of 268 ICU admissions and 384 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 24
Age Groups (years) Cumulative (August 28, 2016 to June 17, 2017)
Hospitalizations ICU Admissions Deaths
Influenza A Total Influenza B Total Total [# (%)] Influenza A and B Total % Influenza A and B Total %
0-4 445 92 537 (8%) 19 7% <5 Table 2 - Footnote x%
5-19 241 96 337 (5%) 20 7% <5 Table 2 - Footnote x%
20-44 294 51 345 (5%) 27 10% 5 1%
45-64 764 139 903 (14%) 82 31% 37 10%
65+ 3949 415 4364 (67%) 120 45% 337 88%
Total 5693 793 6486 (99%) 268 100% 384 100%

Sentinel Hospital Influenza Surveillance

Pediatric Influenza Hospitalizations and Deaths

In weeks 21-24, 14 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Nine of the 14 hospitalizations were associated with influenza B.

To date this season, 586 laboratory-confirmed influenza-associated pediatric hospitalizations were reported by the IMPACT network. Children aged 0-23 months accounted for approximately 37% of hospitalizations and influenza A accounted for 79% of the reported hospitalizations. Among the 126 hospitalizations due to influenza B, 68 (54%) 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, 97 intensive care unit (ICU) admissions have been reported. A total of 65 ICU cases (67%) 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 24

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 87
6-23 mo 131
2-4 yr 149
5-9 yr 113
10-16 yr 106

Figure 7 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2016-17, week 24

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 49 37 3 75
2 27 36 6 60
3 38 37 2 67
4 35 34 5 47
5 38 39 10 57
6 35 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 7 18 9 37
18 10 15 6 28
19 10 10 5 18
20 13 9 4 18
21 5 6 2 10
22 5 4 1 7
23 4 2 0 4
24 0 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

Surveillance for the 2016-2017 influenza season ended on April 30th, 2017.

This season, 1,535 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. A total of 143 intensive care unit (ICU) admissions have been reported. Among ICU cases with available data, 126 cases (88%) reported at least one underlying condition or comorbidity. The median age of patients admitted to the ICU was 71 years. Approximately 86 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 20

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 94
45-64 yr 237
65+ yr 1204

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 20

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= 1535) ICU admissions (n= 143) Deaths (> 86)
20-44 6.1% 6.3% -
45-64 15.4% 18.9% 5.0%
65+ 78.4% 74.8% 96.6%
- Supressed due to small values

Influenza Strain Characterizations

During the 2016-17 influenza season, the National Microbiology Laboratory (NML) has characterized 2,244 influenza viruses [1,614 A(H3N2), 56 A(H1N1), 565 influenza B].  All seasonal influenza A viruses and 20% of influenza B viruses characterized were antigenically or genetically similar to the vaccine strains included in both the trivalent and quadrivalent vaccines. Eighty percent of influenza B viruses characterized were similar to the strain which is only included in the quadrivalent vaccine.

Table 3 – Influenza strain characterizations, Canada, 2016-17, Week 24
Strain Characterization ResultsTable 3 - Footnote 1 Count Description
Influenza A (H3N2)
Antigenically
A/Hong Kong/4801/2014-like		 390 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		 1223

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, one virus belonged to genetic group 3C.3a. Genetic characterization of the 390 influenza A (H3N2) viruses that underwent HI testing determined that 325 viruses belonged to genetic group 3C.2a and 65 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 56 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)		 111 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)		 454 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 1,218 influenza viruses for resistance to oseltamivir, 1,218 influenza viruses for resistance to zanamivir and 266 influenza viruses for resistance to amantadine. All but two influenza A(H3N2) viruses and one of the A(H1N1) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir. All 266 influenza A viruses were resistant to amantadine (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, 2016-17, Week 24
Virus type and subtype Oseltamivir Zanamivir Amantadine
# tested # resistant (%) # tested # resistant (%) # tested # resistant (%)
A (H3N2) 756 2 (0.3%) 755 0 (0%) 215 215 (100%)
A (H3N2v) 1 0 (0%) 1 0 (0%) 1 1 (100%)
A (H1N1) 50 1 (2%) 49 0 (0%) 50 50 (100%)
B 411 0 (0%) 413 0 (0%) N/ATable 4 - Footnote * N/ATable 4 - Footnote *
TOTAL 1218 3 (0.2%) 1218 0 (0%) 266 266 (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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