FluWatch report: April 8 to April 14, 2018 (week 15)

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Public Health Agency of Canada

Date published: 2018-04-13

Related Topics
Overall Summary
  • Overall influenza activity in Canada continued to decrease, but many parts of the country are still reporting localized activity.
  • Two indicators of influenza activity (influenza-like illness and outbreaks) slightly increased from the previous week.
  • Detections of influenza A were greater than those of influenza B.
  • To date this season, the majority of laboratory-confirmed cases, hospitalizations and deaths with influenza have been among adults 65 years of age and older.
  • For more information on the flu, see our Flu(influenza) web page.

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Influenza/Influenza-like Illness Activity (geographic spread)

In week 15, one region in QC reported widespread activity and 23 regions (BC(1), AB(1), MB(2), ON(7), QC(3), NB(2), NL(3), NS(2), PE(1) and NT(1)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-15

Figure 1

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 2018-15
Influenza Surveillance Region Activity Level
Newfoundland - Central Localized
Newfoundland - Eastern Localized
Grenfell Labrador Sporadic
Newfoundland - Western Localized
Prince Edward Island Localized
Nova Scotia - Central (Zone 4) Localized
Nova Scotia - Western (Zone 1) Sporadic
Nova Scotia - Northern (Zone 2) No Activity
Nova Scotia - Eastern (Zone 3) Localized
New Brunswick - Public Health Region 1 Sporadic
New Brunswick - Public Health Region 2 Localized
New Brunswick - Public Health Region 3 Localized
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 Localized
Québec et Chaudieres-Appalaches Sporadic
Centre-du-Québec Widespread
Montréal et Laval Sporadic
Ouest-du-Québec Localized
Montérégie Localized
Ontario - Central East Localized
Ontario - Central West Localized
Ontario - Eastern Localized
Ontario - North East Localized
Ontario - North West Localized
Ontario - South West Localized
Ontario - Toronto Localized
Manitoba - Interlake-Eastern Sporadic
Manitoba - Northern Regional Sporadic
Manitoba - Prairie Mountain Localized
Manitoba - South No Activity
Manitoba - Winnipeg Localized
Saskatchewan - North Sporadic
Saskatchewan - Central Sporadic
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Localized
Alberta - Central Zone Sporadic
Alberta - Calgary Sporadic
Alberta - South Zone Sporadic
British Columbia - Interior Sporadic
British Columbia - Fraser Sporadic
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Localized
British Columbia - Northern No Activity
Yukon No Activity
Northwest Territories - North Sporadic
Northwest Territories - South Localized
Nunavut - Baffin Sporadic
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 15, the overall percentage of tests positive for influenza was 15%, a decrease from the previous week. Overall, laboratory detections of influenza are steadily decreasing. Influenza A accounted for 54% of influenza detections in week 15.

Overall, laboratory detections of influenza are around the 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 2018-15

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 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 2018-15
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 #N/A 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
14 397 143 49 627
15 344 119 54 473

To date this season, 62,062 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 91% 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 2018-15

Figure 3
Figure 3 - Text Description
Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-15
Reporting provincesTable Figure 3 - Footnote 1 Week (April 1, 2018 to April 14, 2018) Cumulative (August 27, 2017 to April 14, 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 53 18 25 10 35 2419 496 1488 435 2974 5393
AB 18 10 3 5 52 5601 218 3985 1398 3272 8873
SK 5 1 1 3 22 1715 60 1148 507 1679 3394
MB 1 1 0 0 27 1129 16 377 736 597 1726
ON 156 10 85 61 82 6013 264 3347 2402 4624 10637
QC 165 0 0 165 116 15124 0 0 15124 12154 27278
NB 66 9 0 57 72 1422 22 207 1193 1098 2520
NS 10 0 0 10 12 505 0 0 505 282 787
PE 2 1 1 0 5 127 7 119 1 161 288
NL 33 0 0 33 16 422 0 3 419 392 814
YT 3 0 3 0 0 75 7 47 21 43 118
NT 1 0 1 0 3 130 4 126 0 55 185
NU 0 0 0 0 0 46 6 40 0 3 49
Canada 513 50 119 344 442 34728 1100 10887 22741 27334 62062
PercentageTable figure 3 Footnote 2 54% 10% 23% 67% 46% 56% 3% 31% 65% 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 50,204 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (50%), and among cases of influenza A(H3N2) (59%) and influenza B (48%). Adults aged 20-64 represent 32% of cases overall and 29% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (883), 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 54% and 31% 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 2018-15
Age groups (years) Cumulative (August 27, 2017 to April 14, 2018)
Influenza A B Influenza A and B
A Total A(H1N1) pdm09 A(H3N2) A (UnS)1 Total # %
0-4 3077 144 551 2382 1452 4529 9%
5-19 2256 126 536 1594 2525 4781 10%
20-44 4150 244 1179 2727 2707 6857 14%
45-64 4558 229 1427 2902 4571 9129 18%
65+ 14610 140 5314 9156 10298 24908 50%
Total 28651 883 9007 18761 21553 50204 100%

Syndromic/Influenza-like Illness Surveillance

Healthcare Practitioners Sentinel Syndromic Surveillance

In week 15, 1.5% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease from the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-15

Number of Sentinels Reporting in Week 15: 159

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 2018-15
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 2.2% 1.5% 1.1% 1.9%
48 2.8% 1.6% 0.8% 2.1%
49 1.7% 1.5% 1.0% 2.5%
50 2.2% 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 4.4% 3.7% 1.7% 5.2%
2 2.8% 3.0% 1.1% 4.5%
3 2.9% 2.5% 1.3% 3.6%
4 3.1% 2.4% 1.7% 3.5%
5 4.0% 2.7% 2.0% 4.4%
6 3.5% 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 1.0% 1.8% 1.3% 2.4%
15 1.5% 1.6% 0.9% 1.9%

Participatory Syndromic Surveillance

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

In week 15, 1,315 participants reported to FluWatchers, of which 2% reported symptoms of cough and fever, and 41% of these consulted a healthcare professional. Among participants who reported cough and fever, 73% reported days missed from work or school, resulting in a combined total of 59 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-15
Number of Participants Reporting Percentage participants reporting Cough and Fever Percentage of participants with cough and fever who consulted a healthcare professional Percentage of participants with cough and fever who reported missed days from work or school Number of missed days from work or school
1315 2% 41% 73% 59

Influenza Outbreak Surveillance

In week 15, 44 laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, 31 were reported in long-term care facilities (LTC), three in hospitals, and 10 in other settings. In addition, two ILI outbreaks were reported in schools. Among the 35 outbreaks with influenza type/subtype reported, 22 (63%) were associated with influenza A, 12 (34%) were associated with influenza B and one outbreak (3%) was associated with a mix of influenza A and B.

To date this season, 1,751 influenza/ILI outbreaks have been reported, of which 1,081 (62%) occurred in LTC facilities. Among the 1,500 outbreaks for which the influenza type/subtype was reported, 825 (55%) were associated with influenza A and 606 (40%) were associated with influenza B, and 69 (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 2018-15

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-15
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 83 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

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,835 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. Among the hospitalizations, 3,260 (67%) were associated with influenza A, and 3,190 cases (66%) were in adults 65 years of age or older.

Additionally, 487 ICU admissions and 265 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 (39%). 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 2018-15

Figure 6
Figure 6 - Text Description
Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, weeks 2017-35 to 2018-15
Age group Total
0-4 297
5-19 220
20-44 309
45-64 819
65+ 3190
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 15, 12 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 67% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07. The number of weekly reported hospitalizations has finally fallen to levels that are near the seven-season average.

To date this season, 1,034 pediatric hospitalizations have been reported by the IMPACT network, 643 (62%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (40%). Among the 391 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 175 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (29%), followed by children aged 5-9 years (26%). Among the ICU cases with available information, 63% were due to influenza A and approximately 47% 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 2018-15

Figure 7
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 2018-15
Age Group Total
0-5 mo 110
6-23 mo 243
2-4 yr 263
5-9 yr 243
10-16 yr 175

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-15

Figure 8
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 2018-15
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 96 35 7 47
5 70 40 11 59
6 74 38 15 79
7 84 40 17 120
8 72 47 25 139
9 68 50 13 153
10 58 48 17 135
11 57 41 18 118
12 35 33 13 89
13 29 32 14 67
14 30 24 12 56
15 12 23 13 56
Figure 8 Footnote 1

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2016-17

Return to figure 8 note 1 referrer

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 3,146 influenza viruses [1,377 A(H3N2), 239 A(H1N1)pdm09 and 1,530 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 3 - Influenza antigenic strain characterizations, Canada, weeks 2017-35 to 2018-15
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 277 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 79 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 239 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) 16 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)
48 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)
1,466 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, 1,021 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 913 A(H3N2) viruses belonged to genetic group 3C.2a, 106 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 356 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 245 belonged to genetic group 3C.2a and 25 viruses belonged to subclade 3C.2a1. The 79 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the remaining seven isolates.

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

Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that 47 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 1,318 influenza viruses for resistance to oseltamivir and 1,314 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 one influenza B viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-15
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 507 1 (0.2%) 503 0 (0%)
A (H1N1) 185 1 (0.5%) 185 0 (0%)
B 626 1 (0.2%) 626 1 (0.2%)
TOTAL 1318 3 (0.2%) 1314 1 (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, the subset of influenza A viruses that were tested for resistance to amantadine were resistant.

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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