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FluWatch report: July 22, 2018 to August 25, 2018 (Weeks 30-34)

Overall Summary

  • Influenza activity is at interseasonal levels across the country.
  • The majority of regions in Canada are reporting no influenza activity.
  • All indicators of influenza activity are at low levels, as expected for this time of year.
  • Influenza A is the most common influenza virus circulating in Canada.
  • This is the last FluWatch report of the 2017-2018 influenza surveillance season. The first report of the 2018-2019 season will be published on September 14, 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: 2018-08-31

Related Topics

Influenza/Influenza-like Illness Activity (geographic spread)

In week 34, two regions in AB(1) and QC(1) reported sporadic activity. The majority of regions (42) reported no activity. Nine regions did not report data for week 34.

Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-34
Figure 1. Text version below.
Figure 1 - Text description
Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-34
Influenza Surveillance Region Activity Level
Newfoundland - Central No Activity
Newfoundland - Eastern No Activity
Grenfell Labrador No Activity
Newfoundland - Western No Activity
Prince Edward Island No Activity
Nova Scotia - Central (Zone 4) No Data
Nova Scotia - Western (Zone 1) No Data
Nova Scotia - Northern (Zone 2) No Data
Nova Scotia - Eastern (Zone 3) No Data
New Brunswick - Public Health Region 1 No Activity
New Brunswick - Public Health Region 2 No Activity
New Brunswick - Public Health Region 3 No Activity
New Brunswick - Public Health Region 4 No Activity
New Brunswick - Public Health Region 5 No Activity
New Brunswick - Public Health Region 6 No Activity
New Brunswick - Public Health Region 7 No Activity
Nord-est Québec No Activity
Québec et Chaudieres-Appalaches No Activity
Centre-du-Québec Sporadic
Montréal et Laval No Activity
Ouest-du-Québec No Activity
Montérégie No Activity
Ontario - Central East No Activity
Ontario - Central West No Activity
Ontario - Eastern No Activity
Ontario - North East No Activity
Ontario - North West No Activity
Ontario - South West No Activity
Ontario - Toronto No Activity
Manitoba - Interlake-Eastern No Data
Manitoba - Northern Regional No Data
Manitoba - Prairie Mountain No Data
Manitoba - South No Data
Manitoba - Winnipeg No Data
Saskatchewan - North No Activity
Saskatchewan - Central No Activity
Saskatchewan - South No Activity
Alberta - North Zone No Activity
Alberta - Edmonton No Activity
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 weeks 30 to 34, a total of 45 laboratory detections of influenza were reported, the majority of which were influenza A. In week 34, the percentage of tests positive for influenza was 0.4%. Overall, laboratory detections of influenza are at interseasonal levels.

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 2018-34
Figure 2. 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 2018-34
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 8 13 82
20 51 5 14 38
21 40 7 14 27
22 22 11 11 14
23 8 5 1 8
24 8 1 3 6
25 5 1 1 7
26 2 8 1 6
27 2 1 2 2
28 5 2 2 0
29 5 1 2 0
30 5 4 0 1
31 3 2 2 3
32 2 4 1 2
33 3 2 0 4
34 4 1 2 0

This season, 64,403 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 2018-34
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 2018-34
Reporting provincesTable Figure 3 - Footnote 1 Week (July 22, 2018 to August 25, 2018) Cumulative (August 27, 2017 to August 25, 2018)
Influenza A B Influenza A B Influenza A & B Total
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
BC 6 2 4 0 1 2492 521 1524 447 3022 5514
AB 5 0 5 0 2 5722 283 4012 1427 3399 9121
SK 2 0 1 1 1 1739 69 1135 535 1718 3457
MB 0 0 0 0 0 1137 22 378 737 640 1777
ON 13 3 3 7 2 6368 304 3484 2580 4838 11206
QC 6 0 0 6 5 15518 0 0 15518 12356 27874
NB 0 0 0 0 0 1713 36 249 1428 1282 2995
NS 2 0 0 2 0 567 0 0 567 302 869
PE 0 0 0 0 0 146 8 134 4 171 317
NL 1 0 0 1 0 480 0 3 477 436 916
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 6 52
Canada 35 5 13 17 11 36134 1260 11133 23741 28269 64403
PercentageTable figure 3 Footnote 2 76% 14% 37% 49% 24% 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.

This season, detailed information on age and type/subtype has been received for 55,059 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (49%), and among cases of influenza A(H3N2) (57%) and influenza B (46%). 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 (1,108), 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 51% 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 2018-34
Age groups (years) Cumulative (August 27, 2017 to August 25, 2018)
Influenza A B Influenza A and B
A Total A(H1N1) pdm09 A(H3N2) A (UnS)1 Total # %
0-4 3375 202 682 2491 1616 4991 9%
5-19 2574 157 709 1708 2993 5567 10%
20-44 4597 297 1387 2913 3051 7648 14%
45-64 4987 270 1597 3120 5098 10085 18%
65+ 15743 182 5882 9679 11025 26768 49%
Total 31276 1108 10257 19911 23783 55059 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 34, 0.5% 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 2018-34

Number of Sentinels Reporting in Week 34: 120

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 2018-34
Report week 2017-18 Average 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 3.1% 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 0.9% 1.2% 0.9% 1.4%
21 0.8% 0.9% 0.3% 1.3%
22 0.9% 0.8% 0.6% 1.0%
23 0.7% 0.9% 0.6% 1.2%
24 0.8% 0.7% 0.4% 1.0%
25 0.6% 1.2% 0.5% 1.6%
26 0.7% 0.8% 0.4% 1.4%
27 0.7% 0.8% 0.4% 1.5%
28 0.6% 1.0% 0.6% 1.9%
29 0.5% 0.8% 0.5% 1.1%
30 0,4% 0,5% 0,3% 0,7%
31 0,7% 0,9% 0,3% 1,4%
32 0,4% 1,0% 0,6% 1,6%
33 0,5% 1,2% 0,4% 2,1%
34 0,5% 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. Click here to learn more about the FluWatchers program.

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

No influenza or ILI outbreaks were reported in weeks 30-34.

This season, 1,798 influenza/ILI outbreaks have been reported, of which 1,107 (62%) occurred in LTC facilities. Among the 1,536 outbreaks for which the influenza type/subtype was reported, 846 (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 2018-34
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 2018-34
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
21 0 1 0
22 0 1 0
23 0 0 0
24 0 0 0
25 0 0 0
26 0 0 1
27 0 0 0
28 0 0 0
29 0 0 0
30 0 0 0
31 0 0 0
32 0 0 0
33 0 0 0
34 0 0 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

This season, 5,176 influenza-associated hospitalizations were reported by participating provinces and territoriesfigure 6 note 1. Among the hospitalizations, 3,446 (67%) were associated with influenza A, and 3,380 cases (65%) were in adults 65 years of age or older.

Additionally, 529 ICU admissions and 302 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (43%), followed by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (86%).

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-34
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 2018-34
Age group Total
0-4 yr 329
5-19 yr 238
20-44 yr 340
45-64 yr 889
65+ yr 3380
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 weeks 30-34, two laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network.

This season, 1,085 pediatric hospitalizations have been reported by the IMPACT network, 681 (63%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 404 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 203 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (30%), followed by children aged 5-9 years (26%). Among the ICU cases with available information, 63% were due to influenza A and approximately 42% had no reported previous or concurrent medical conditions. All but one of the 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 2018-34
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 2018-34
Age Group Total
0-5 mo 114
6-23 mo 252
2-4 yr 272
5-9 yr 265
10-16 yr 182
Figure 8 – Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-34
Figure 8. Text version below.

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

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 2018-34
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 73 38 15 79
7 83 40 17 120
8 72 47 25 139
9 68 50 13 153
10 60 48 17 135
11 57 41 18 118
12 33 33 13 89
13 28 32 14 67
14 30 24 12 56
15 14 23 13 56
16 9 20 10 41
17 12 16 8 37
18 9 14 4 28
19 5 10 5 18
20 2 10 4 19
21 4 5 2 10
22 1 4 1 8
23 1 2 0 5
24 2 2 0 5
25 0 1 0 3
26 0 1 0 3
27 0 1 0 2
28 0 1 0 2
29 1 0 0 2
30 2 0 0 1
31 0 0 0 0
32 0 0 0 1
33 0 0 0 0
34 0 1 0 2

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 3,857 influenza viruses [1,576 A(H3N2), 336 A(H1N1)pdm09 and 1,945 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 2018-29
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 309

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 102

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 334

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)		 26

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)		 57

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)		 1862

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, 1,165 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 1,044 A(H3N2) viruses belonged to genetic group 3C.2a, 118 viruses belonged to subclade 3C.2a1 and three viruses belonged to the clade 3C.3a.

Additionally, of the 411 influenza A(H3N2) viruses that were antigenically characterized, 282 belonged to genetic group 3C.2a and 27 viruses belonged to subclade 3C.2a1. The 102 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

Among the viruses characterized antigenically as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that 57 viruses had a two amino acid deletion in the HA gene.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,767 influenza viruses for resistance to oseltamivir and 1,763 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 2018-29
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 600 1 (0.2%) 596 0 (0%)
A (H1N1)pdm09 278 1 (0.4%) 278 0 (0%)
B 889 1 (0.1%) 889 2 (0.2%)
Total 1767 3 (0.2%) 1763 2 (0.1%)

Note: Since the 2009 pandemic, the majority of 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 for the 2017-2018 Season – Notes and Definitions

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

† 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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