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FluWatch report: May 13 to May 19, 2018 (Week 20)

Overall Summary
  • Nationally, the 2017-18 influenza season has ended.
  • The majority of regions in Canada are reporting sporadic or no influenza activity.
  • All indicators of influenza activity are either near or below average for this time of year.
  • This is the last weekly report for the 2017-18 season. FluWatch will publish monthly reports over the summer. The next report will be published June 29, 2018.
  • Influenza and other respiratory viruses will be monitoried weekly and results will be reported every Thursday in the Respiratory Virus Detections in Canada Report.
  • For more information on the flu, see our Flu(influenza) web page.

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Organization:

Public Health Agency of Canada

Date published: 2018-05-25

Related Topics

Influenza/Influenza-like Illness Activity (geographic spread)

In week 20, four regions in Ontario reported localized activity. The provinces of BC and PE and the territories reported no activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-20
Figure 1. Text version below.

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
Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-20
Influenza Surveillance Region Activity Level
Newfoundland - Central  Sporadic
Newfoundland - Eastern  No Activity
Grenfell Labrador Sporadic
Newfoundland - Western  No Activity
Prince Edward Island No Activity
Nova Scotia - Central (Zone 4) Sporadic
Nova Scotia - Western (Zone 1) Sporadic
Nova Scotia - Northern (Zone 2) No Activity
Nova Scotia - Eastern (Zone 3) Sporadic
New Brunswick - Public Health Region 1 Sporadic
New Brunswick - Public Health Region 2 Sporadic
New Brunswick - Public Health Region 3 Sporadic
New Brunswick - Public Health Region 4 No Activity
New Brunswick - Public Health Region 5 No Activity
New Brunswick - Public Health Region 6 Sporadic
New Brunswick - Public Health Region 7 Sporadic
Nord-est Québec No Data
Québec et Chaudieres-Appalaches No Data
Centre-du-Québec No Data
Montréal et Laval No Data
Ouest-du-Québec No Data
Montérégie  No Data
Ontario - Central East Localized
Ontario - Central West Localized
Ontario - Eastern Localized
Ontario - North East Sporadic
Ontario - North West  Sporadic
Ontario - South West  Localized
Ontario - Toronto Sporadic
Manitoba - Interlake-Eastern  No Activity
Manitoba - Northern Regional No Activity
Manitoba - Prairie Mountain No Activity
Manitoba - South No Activity
Manitoba - Winnipeg Sporadic
Saskatchewan - North  No Activity
Saskatchewan - Central Sporadic
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Sporadic
Alberta - Central Zone  No Activity
Alberta - Calgary Sporadic
Alberta - South Zone  No Activity
British Columbia - Interior No Activity
British Columbia - Fraser  No Activity
British Columbia - Vancouver Coastal No Activity
British Columbia - Vancouver Island No Activity
British Columbia - Northern No Activity
Yukon No Activity
Northwest Territories - North No Activity
Northwest Territories - South No Activity
Nunavut - Baffin No Activity
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 20, the percentage of tests positive for influenza was 3.5%, a decrease from the previous week. The percentage of tests positive for influenza has been below 5% for two consecutive weeks.This indicates the end of the 2017-18 influenza season in Canada.

In week 20, a total of 106 laboratory detections of influenza were reported and influenza A accounted for 64% of influenza detections. Overall, laboratory detections of influenza are below expected levels for this time of year.

Overall, laboratory detections of influenza are below average for this time of year. For data on other respiratory virus detections, see the Respiratory Virus Detections in Canada Report.

Figure 2 - Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2017-35 to 2018-20

Figure 1. Text version below.

The shaded area indicates weeks where the positivity rate was at least 5% and a minimum of 15 positive tests were observed, signalling the period 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, weeks 2017-35 to 2018-20
Report Week A(Unsubtyped) A(H3N2) A(H1N1)pdm09 Influenza B
35 3 20 6 5
36 7 28 1 3
37 7 14 13 4
38 18 31 3 5
39 18 53 1 8
40 24 41 1 5
41 32 50 0 11
42 27 73 1 15
43 44 107 3 21
44 52 114 3 30
45 71 153 7 47
46 113 187 13 75
47 157 272 13 112
48 259 417 33 190
49 370 544 16 274
50 523 633 16 473
51 800 864 51 719
52 1105 856 33 1008
1 1836 925 60 1539
2 1987 808 49 1730
3 1649 870 80 1912
4 1675 632 57 1802
5 1664 542 54 2125
6 1819 506 49 2383
7 1754 405 63 2443
8 1642 279 51 2354
9 1437 325 51 2057
10 1023 265 80 1714
11 807 246 73 1387
12 551 189 76 966
13 458 183 40 767
14 436 143 49 661
15 370 127 57 500
16 302 84 29 322
17 214 62 35 238
18 153 51 44 129
19 89 7 13 81
20 51 5 12 38

To date this season, 64,154 laboratory-confirmed influenza detections have been reported, of which 56% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 90% of subtyped 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, weeks 2017-35 to 2018-20
Figure 3. Text version below.
Figure 3 - Text description
Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-20
Reporting provincesTable Figure 3 - Footnote 1 Week (May 13, 2018 to May 19, 2018) Cumulative (August 27, 2017 to May 19, 2018)
Influenza A B Influenza A B A & B
A Total A(H1N1)pdm09 A(H3N2) A(UnS)Table Figure 3 - Footnote 3 B Total A Total A(H1N1)pdm09 A(H3N2) A(UnS)Table Figure 3 - Footnote 3 B Total Total
BC 1 0 0 1 0 2476 516 1515 445 3021 5497
AB 8 7 0 1 9 5675 260 3994 1421 3387 9062
SK 3 0 1 2 1 1759 70 1151 538 1733 3492
MB 1 1 0 0 2 1134 20 378 736 637 1771
ON 14 2 0 12 6 6317 293 3466 2558 4828 11145
QC 21 0 0 21 3 15473 0 0 15473 12332 27805
NB 14 2 4 8 14 1684 33 244 1407 1257 2941
NS 4 0 0 4 1 555 0 0 555 301 856
PE 0 0 0 0 0 146 8 134 4 171 317
NL 2 0 0 2 2 478 0 3 475 435 913
YT 0 0 0 0 0 76 7 48 21 43 119
NT 0 0 0 0 0 130 4 126 0 56 186
NU 0 0 0 0 0 46 6 40 0 4 50
Canada 68 12 5 51 38 35949 1217 11099 23633 28205 64154
PercentageTable figure 3 Footnote 2 64% 18% 7% 75% 36% 56% 3% 31% 66% 44% 100%
Table Figure 3 - Footnote 1

Specimens from NT, YT, and NU are sent to reference laboratories in other provinces.

Return to Table Figure 3 - Footnote 1 referrer*

Table Figure 3 - Footnote 2

Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections.

Return to Table Figure 3 - Footnote 2 referrer

Table Figure 3 - Footnote 3

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to first Table Figure 3 - Footnote 3 referrer

Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Cumulative data includes updates to previous weeks.

To date this season, detailed information on age and type/subtype has been received for 54,915 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (48%), and among cases of influenza A(H3N2) (57%) and influenza B (46%). Adults aged 20-64 represent 32% of cases overall and 30% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (1,002), the majority of influenza A(H1N1)pdm09 cases are among adults less than 65 years of age, with adults aged 20-64 and children 0-19 years accounting for 52% and 32% of cases respectively.

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2017-35 to 2018-20
Age groups (years) Cumulative (August 27, 2017 to May 19, 2018)
Influenza A B Influenza A and B
A Total A(H1N1) pdm09 A(H3N2) A (UnS)table 1 note 1 Total # %
0-4 3348 178 690 2480 1624 4972 9%
5-19 2566 145 724 1697 2998 5564 10%
20-44 4597 274 1430 2893 3055 7652 14%
45-64 4977 245 1638 3094 5123 10100 18%
65+ 15621 160 5841 9620 11006 26627 48%
Total 31109 1002 10323 19784 23806 54915 100%
Table 1 Notes
Table 1 Note 1

UnS: unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available

Return to table 1 note 1 referrer

 

Syndromic/Influenza-like Illness Surveillance

Healthcare Practitioners Sentinel Syndromic Surveillance

In week 20, 1.1% of visits to healthcare professionals were due to influenza-like illness (ILI).

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-20

Number of Sentinels Reporting in Week 20: 155

Figure 4. Text version below.

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2016-17

Figure 4 - Text description
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-20
Semaine de déclaration 2017-18 Moyenne Min Max
35 0.4% 0.8% 0.5% 1.2%
36 0.5% 0.8% 0.7% 1.0%
37 0.7% 0.9% 0.7% 1.0%
38 0.7% 1.1% 1.0% 1.4%
39 1.1% 1.1% 0.9% 1.4%
40 1.3% 1.3% 0.9% 1.6%
41 1.7% 1.4% 0.9% 2.4%
42 1.2% 1.4% 1.0% 1.9%
43 1.6% 1.3% 1.0% 1.5%
44 1.5% 1.3% 0.9% 1.6%
45 1.8% 1.3% 1.2% 1.5%
46 1.7% 1.6% 1.0% 2.0%
47 2.1% 1.5% 1.1% 1.9%
48 2.5% 1.6% 0.8% 2.1%
49 1.7% 1.5% 1.0% 2.5%
50 2.1% 2.3% 1.3% 3.7%
51 2.6% 2.5% 1.6% 4.1%
52 4.0% 4.5% 1.7% 7.1%
1 4.5% 3.7% 1.7% 5.2%
2 2.7% 3.0% 1.1% 4.5%
3 2.7% 2.5% 1.3% 3.6%
4 2.9% 2.4% 1.7% 3.5%
5 4.0% 2.7% 2.0% 4.4%
6 3.4% 2.7% 2.1% 3.3%
7 3.4% 2.4% 1.7% 3.0%
8 3.0% 2.3% 1.9% 2.7%
9 2.8% 2.2% 1.8% 2.7%
10 1.7% 2.1% 1.8% 2.7%
11 1.2% 2.1% 1.7% 2.7%
12 1.6% 1.8% 1.1% 2.7%
13 1.7% 1.7% 1.2% 2.6%
14 0.9% 1.8% 1.3% 2.4%
15 1.3% 1.6% 0.9% 1.9%
16 1.3% 1.5% 1.0% 1.9%
17 1.5% 1.5% 0.9% 2.2%
18 1.3% 1.2% 0.8% 1.6%
19 1.4% 1.3% 1.0% 1.7%
20 1.1% 1.2% 0.9% 1.4%
21   0.9% 0.3% 1.3%
22   0.8% 0.6% 1.0%
23   0.9% 0.6% 1.2%
24   0.7% 0.4% 1.0%
25   1.2% 0.5% 1.6%
26   0.8% 0.4% 1.4%
27   0.8% 0.4% 1.5%
28   1.0% 0.6% 1.9%
29   0.8% 0.5% 1.1%
30   0.5% 0.3% 0.7%
31   0.9% 0.3% 1.4%
32   1.0% 0.6% 1.6%
33   1.2% 0.4% 2.1%
34   0.7% 0.5% 0.9%

Participatory Syndromic Surveillance

FluWatchers is a participatory ILI surveillance system that relies on weekly voluntary submissions of syndromic information from Canadians across Canada.

FluWatchers surveillance has ended for the 2017-18 season.

If you are interested in becoming a FluWatcher for the 2018-19 season, sign up today.

Influenza Outbreak Surveillance

In week 20, one outbreak in a long term care facility due to influenza A(H3N2) was reported.

To date this season, 1,795 influenza/ILI outbreaks have been reported, of which 1,105 (62%) occurred in LTC facilities. Among the 1,533 outbreaks for which the influenza type/subtype was reported, 843 (55%) were associated with influenza A and 618 (40%) were associated with influenza B, and 72 (5%) were associated with a mix of A and B.

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-20

Figure 5. Text version below.
Figure 5 - Text description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-20
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 1 0
37 0 0 0
38 0 2 0
39 0 1 1
40 1 0 0
41 0 0 1
42 0 2 1
43 3 1 1
44 0 1 0
45 3 1 4
46 0 2 5
47 0 2 5
48 9 11 7
49 4 14 12
50 9 31 16
51 11 48 28
52 5 72 23
1 12 110 38
2 18 99 48
3 14 84 45
4 13 65 24
5 9 55 19
6 10 77 31
7 11 58 28
8 8 60 22
9 8 84 16
10 12 46 10
11 2 44 12
12 8 32 10
13 5 30 8
14 9 18 8
15 3 31 10
16 1 10 4
17 0 6 3
18 3 4 4
19 2 2 1
20 0 1 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 5,111 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. Among the hospitalizations, 3,403 (67%) were associated with influenza A, and 3,340 cases (65%) were in adults 65 years of age or older.

Additionally, 513 ICU admissions and 295 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (44%), followed by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (85%).

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-20

Figure 6. Text version below.
Figure 6 - Text description
Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-20
Age group Total
0-4 322
5-19 238
20-44 337
45-64 874
65+ 3340
Figure 6 note 1

Influenza-associated hospitalizations are reported by NL, PE, NS, NB, MB, AB, YT and NT. Only hospitalizations that require intensive medical care are reported by SK.

Return to figure 6 note 1 referrer

Pediatric Influenza Hospitalizations and Deaths

In week 20, one laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations was reported by the Immunization Monitoring Program Active (IMPACT) network. The number of weekly reported hospitalizations are below the seven-season average.

To date this season, 1,078 pediatric hospitalizations have been reported by the IMPACT network, 667 (62%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 403 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 185 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (31%), followed by children aged 5-9 years (26%). Among the ICU cases with available information, 62% were due to influenza A and approximately 46% had no reported previous or concurrent medical conditions. All but one reported deaths were among children over the age of two.

Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, weeks 2017-35 to 2018-20

Figure 7. Text version below.
Figure 7 - Text description
Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, weeks 2017-35 to 2018-20
Age Group Total
0-5 mo 112
6-23 mo 248
2-4 yr 268
5-9 yr 261
10-16 yr 181

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-20

Figure 8. Text version below.

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2016-18

Figure 8 - Text description
Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-20
Report week 2017-18 Average Min Max
35 0 0 0 0
36 1 0 0 1
37 0 0 0 2
38 1 0 0 2
39 2 1 0 3
40 0 0 0 2
41 3 1 0 2
42 1 1 0 4
43 7 1 0 3
44 1 3 1 6
45 4 3 2 4
46 7 5 1 13
47 13 4 0 9
48 17 9 2 23
49 23 15 3 28
50 25 23 4 47
51 38 32 4 72
52 60 47 7 92
1 57 40 5 75
2 38 35 4 62
3 52 38 4 67
4 93 35 7 47
5 70 40 11 59
6 74 38 15 79
7 83 40 17 120
8 72 47 25 139
9 67 50 13 153
10 60 48 17 135
11 57 41 18 118
12 33 33 13 89
13 29 32 14 67
14 31 24 12 56
15 13 23 13 56
16 9 20 10 41
17 13 16 8 37
18 10 14 4 28
19 4 10 5 18
20 1 10 4 19
21   5 2 10
22   4 1 8
23   2 0 5
24   2 0 5
25   1 0 3
26   1 0 3
27   1 0 2
28   1 0 2
29   0 0 2
30   0 0 1
31   0 0 0
32   0 0 1
33   0 0 0
34   1 0 2

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 3,723 influenza viruses [1,535 A(H3N2), 306 A(H1N1)pdm09 and 1,882 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition (HI) assay during the 2017-18 season, most viruses were antigenically similar to the cell-culture propagated reference strains recommended by WHO.

Table 2 - Influenza antigenic strain characterizations, Canada, weeks 2017-35 to 2018-20
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 302 Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent vaccine.
Reduced titer to A/Hong Kong/4801/2014 95 These A(H3N2) viruses reacted poorly with antisera raised against cell-propagated A/Hong Kong/4801/2014, suggesting some antigenic differences.
Influenza A (H1N1)pdm09
A/Michigan/45/2015-like 306 Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1)pdm09 component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.
Influenza B
B/Brisbane/60/2008-like
(Victoria lineage)		 24 Viruses antigenically similar to B/Brisbane/60/2008. B/Brisbane/60/2008 is the influenza B component of the 2017-18 Northern Hemisphere’s trivalent and quadrivalent influenza vaccine.
Reduced titer to B/Brisbane/60/2008
(Victoria lineage)		 54 These B/Victoria lineage viruses reacted poorly with antisera raised against cell-propagated B/Brisbane/60/2008, suggesting some antigenic differences.
B/Phuket/3073/2013-like
(Yamagata lineage)		 1804 Viruses antigenically similar to B/Phuket/3073/2013, the additional influenza B component of the 2017-18 Northern Hemisphere quadrivalent influenza vaccine.

Genetic Characterization of A(H3N2) viruses

During the 2017-18 season, 1,138 A(H3N2) viruses did not grow to sufficient titers for antigenic characterization by HI assay. Therefore, genetic characterization was performed to determine to which genetic group they belong. Sequence analysis showed that 1,018 A(H3N2) viruses belonged to genetic group 3C.2a, 117 viruses belonged to subclade 3C.2a1 and three viruses belonged to the clade 3C.3a.

Additionally, of the 397 influenza A(H3N2) viruses that were antigenically characterized, 276 belonged to genetic group 3C.2a and 26 viruses belonged to subclade 3C.2a1. The 95 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a.

A/Hong Kong/4801/2014-like virus belongs to genetic group 3C.2a and is the influenza A/H3N2 component of the 2017-18 Northern Hemisphere influenza vaccine.

Genetic Characterization of Influenza B viruses

Of the 78 influenza B viruses characterized as B/ B/Brisbane/60/2008-like, 24 viruses were antigenically similar to the vaccine strain B/Brisbane/60/2008. Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that 53 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the remaining virus isolate.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,565 influenza viruses for resistance to oseltamivir and 1,561 viruses for resistance to zanamivir. All but three viruses (1 A(H1N1)pdm09,1 A(H3N2) and 1 influenza B) were sensitive to oseltamivir and all but two influenza B viruses were sensitive to zanamivir (Table 3). The A(H1N1)pdm09 virus resistant to oseltamivir had a H275Y mutation.

Table 3 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-20
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 558 1 (0.2%) 554 0 (0%)
A (H1N1) 235 1 (0.4%) 235 0 (0%)
B 772 1 (0.1%) 772 2 (0.3%)
TOTAL 1565 3 (0.2%) 1561 2 (0.1%)

Note: Since the 2009 pandemic, all circulating influenza A viruses have been resistant to amantadine, and it is therefore not currently recommended for use in the treatment of influenza. During the 2017-18 season, all but eight influenza A viruses that were tested for resistance to amantadine were resistant.

Provincial and International Influenza Reports

Provincial Influenza Reports

International Influenza Reports

FluWatch Surveillance System Description and Definitions, 2017-18

The FluWatch report is compiled from a number of data sources. Surveillance information contained in this report is a reflection of the surveillance data available to FluWatch at the time of production. Delays in reporting of data may cause data to change retrospectively.

Influenza/Influenza-like Illness (ILI) Activity

Influenza/ILI activity levels, as represented on the map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, primary care consultations for ILI and reported outbreaks. ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls, and the determination of an increase is based on the assessment of the provincial/territorial epidemiologist. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.

Influenza/ILI Activity Level definitions

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†
3 = Localized:
(1) evidence of increased ILI*; (2) lab confirmed influenza detection(s); (3) outbreaks in schools, hospitals, residential
institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance region†
4 = Widespread:
(1) evidence of increased ILI*; (2) lab confirmed influenza detection(s);(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 region†;

* More than just sporadic as determined by the provincial/territorial epidemiologist. †Influenza surveillance regions within the province or territory as defined by the provincial/territorial epidemiologist

Laboratory-Confirmed Influenza Detections

Provincial, regional and some hospital laboratories report the weekly number of tests and detections of influenza and other respiratory viruses. Provincial public health laboratories submit demographic information for cases of influenza. This case-level data represents a subset of influenza detections reported through aggregate reporting. Specimens from NT, YT, and NU are sent to reference laboratories in the provinces for testing. Cumulative data includes updates to previous weeks. Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Syndromic/Influenza-like Illness Surveillance

FluWatch maintains a network of primary care practitioners who report the weekly proportion of ILI cases seen in their practice. Independent sentinel networks in BC, AB, and SK compile their data for reporting to FluWatch. Not all sentinel physicians report every week.

Definition of 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 years of age, gastrointestinal symptoms may also be present. In patients under 5 or 65 years and older, fever may not be prominent.

Influenza Outbreak Surveillance

Outbreaks of influenza or ILI are reported from all provinces and territories, according to the definitions below. However, reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions. All provinces and territories with the exception of NU report influenza outbreaks in long-term care facilities. All provinces and territories with the exception of NU and QC report outbreaks in hospitals.

Outbreak definitions:

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.
Hospitals and residential institutions:
two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case of influenza. Residential institutions include but are 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 of influenza; i.e. closed communities.

Serious Outcome Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

Influenza-associated hospitalizations and deaths are reported by 8 Provincial and Territorial Ministries of Health (excluding BC, NU, ON and QC). The hospitalization or death does not have to be attributable to influenza, a positive laboratory test is sufficient for reporting. Only hospitalizations that require intensive medical care are reported by SK.

Due to changes in participating provinces and territories, comparisons to previous years should be done with caution.

Pediatric Influenza Hospitalizations and Deaths

The Immunization Monitoring Program Active (IMPACT) network reports the weekly number of hospitalizations with influenza among children admitted to one of the 12 participating paediatric hospitals in 8 provinces. These represent a subset of all influenza-associated pediatric hospitalizations in Canada.

Influenza Strain Characterizations and Antiviral Resistance

Provincial public health laboratories send a subset of influenza virus isolates to the National Microbiology Laboratory for strain characterization and antiviral resistance. These represent a subset of all influenza detections in Canada and the proportion of isolates of each type and subtype is not necessarily representative of circulating viruses.

Antigenic strain characterization data reflect the results of hemagglutination inhibition (HI) testing compared to the reference influenza strains recommended by WHO. Genetic strain characterization data are based on analysis of the sequence of the viral hemagglutinin (HA) gene.

 

Antiviral resistance testing is conducted by phenotypic and genotypic methods on influenza virus isolates submitted to the National Microbiology Laboratory. All isolates are tested for oseltamivir and zanamivir and a subset are tested for resistance to amantadine.

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).

This report is available on the Government of Canada Influenza webpage.

We would like to thank all the FluWatch surveillance partners who are participating in this year's influenza surveillance program.

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