FluWatch report: January 14, 2018 to January 20, 2018 (week 3)

Overall Summary
  • Overall, influenza activity in Canada remains high but there is some indication that activity is starting to slow down.
  • Most indicators remain in the higher range of expected levels for this time of year.
  • In week 3, the percentage of laboratory test positive for influenza B continued to increase while the percentage of laboratory test positive for influenza A remained stable.
  • The majority of influenza detections continue to be A(H3N2), although 40% of detections were influenza B in week 03.
  • To date this season, the majority of lab confirmations, hospitalizations and deaths 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 03, a similar number of regions reported localized or widespread influenza activity compared to the previous week. Among the 53 regions reporting data for week 03, 11 regions (BC(2), ON(4), QC(4), and PE (1)) reported widespread activity, and 23 regions (BC(1), AB(4), SK(2), MB(1), ON(3), QC(2), NB(4), NS(3), NL(2), and NT(1)) reported localized activity.

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Public Health Agency of Canada

Date published: 2018-01-26

Related Topics

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-03

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 2018-03
Influenza Surveillance Region Activity Level
Newfoundland - Central Sporadic
Newfoundland - Eastern Localized
Grenfell Labrador No Activity
Newfoundland - Western Localized
Prince Edward Island Widespread
Nova Scotia - Central (Zone 4) Localized
Nova Scotia - Western (Zone 1) Localized
Nova Scotia - Northern (Zone 2) No Activity
Nova Scotia - Eastern (Zone 3) Localized
New Brunswick - Public Health Region 1 Localized
New Brunswick - Public Health Region 2 Localized
New Brunswick - Public Health Region 3 Localized
New Brunswick - Public Health Region 4 Sporadic
New Brunswick - Public Health Region 5 Sporadic
New Brunswick - Public Health Region 6 Sporadic
New Brunswick - Public Health Region 7 Localized
Nord-est Québec Localized
Québec et Chaudieres-Appalaches Widespread
Centre-du-Québec Widespread
Montréal et Laval Widespread
Ouest-du-Québec Widespread
Montérégie Localized
Ontario - Central East Widespread
Ontario - Central West Widespread
Ontario - Eastern Localized
Ontario - North East Localized
Ontario - North West Widespread
Ontario - South West Widespread
Ontario - Toronto Localized
Manitoba - Interlake-Eastern Sporadic
Manitoba - Northern Regional Sporadic
Manitoba - Prairie Mountain Sporadic
Manitoba - South Sporadic
Manitoba - Winnipeg Localized
Saskatchewan - North Localized
Saskatchewan - Central Localized
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Localized
Alberta - Central Zone Localized
Alberta - Calgary Localized
Alberta - South Zone Localized
British Columbia - Interior Localized
British Columbia - Fraser Widespread
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Widespread
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Localized
Nunavut - Baffin No Activity
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 03, the percentage of tests positive for influenza increased slightly from 29% in week 02 to 31% in week 03. This increase is mainly driven by influenza B activity: the percentage of test positive for influenza B increased from 11% in week 02 to 13% in week 03. Influenza B detections to date are higher than has been observed over the past seven seasons.

The percentage of test positive for influenza A remained stable at 18% since week 02. The stablization of influenza A detections over the past two weeks may indicate that the peak of the season for influenza A detections occurred in week 01.

The number (2,533) and percentage (18%) of influenza A detections for week 03 are within the range of expected levels for this time of year. The number (1,835) and percentage of tests (13%) positive for influenza B in week 03 continue to be well above expected levels 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 2018-03

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 2018-03
Report Week A(Unsubtyped) A(H3) A(H1)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 807 49 1730
3 1764 701 68 1835

To date this season, 24,749 laboratory-confirmed influenza detections have been reported, of which 67% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 94% 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 2018-03

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 2018-03
Reporting
provincesTable Figure 3 - Footnote 1
Week (January 14, 2018 to January 20, 2018) Cumulative (August 27, 2017 to January 20, 2018)
Influenza A B Influenza A B A & B
Total
A
Total
A
(H1)pdm09
A
(H3)
A(UnS)Table Figure 3 - Footnote 3 B
Total
A
Total
A
(H1)pdm09
A
(H3)
A(UnS)Table Figure 3 - Footnote 3 B
Total
BC 410 54 269 87 330 1401 197 846 358 1322 2723
AB 201 4 143 54 173 4852 82 3583 1187 1787 6639
SK 76 2 63 11 49 1161 32 809 320 353 1514
MB 141 0 19 122 19 897 6 311 580 77 974
ON 462 8 247 207 404 2083 75 1172 836 1426 3509
QC 1119 0 0 1119 776 5299 0 0 5299 2905 8204
NB 85 0 0 85 68 549 0 84 465 125 674
NS 40 0 0 40 13 152 0 0 152 30 182
PE 5 0 5 0 27 47 2 45 0 66 113
NL 9 0 0 9 2 42 0 3 39 19 61
YT 10 1 3 6 2 18 1 11 6 35 53
NT 11 1 10 0 6 110 1 109 0 15 125
NU 5 0 5 0 1 21 0 21 0 2 12
Canada 2574 70 764 1740 1870 16632 396 6994 9242 8162 24794
PercentageTable Figure 3 - Footnote 2 58% 3% 30% 68% 42% 67% 2% 42% 56% 33% 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 21,369 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 50% have been reported in adults 65 years of age and older. Among cases of influenza A(H3N2), adults 65 years of age and older represented 53% of cases. Cases of influenza B this season were distributed more evenly across all age-groups, but the largest proportion of cases was still among adults 65 years of age and older (46%), followed by adults 45-64 years of age (22%).

Table 1 - Weekly and cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, weeks 2017-35 to 2018-03
Age groups (years) Cumulative (August 27, 2017 to January 20, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 1208 64 469 675 391 1599 7%
5-19 1117 55 512 550 808 1925 9%
20-44 2323 101 1001 1221 971 3294 15%
45-64 2436 88 1059 1289 1522 3958 19%
65+ 7454 47 3475 3932 3139 10593 50%
Total 14538 355 6516 7667 6831 21369 100%
Table 1 Footnote 1

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

Return to table 1 footnote 1 referrer

Syndromic/Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 03, 3% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease compared to the previous week, and slightly above the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-03

Number of Sentinels Reporting in Week 03: 153

Figure 4

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2012-13 to 2017-18

Figure 4 - Text Description
Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-03
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 2.7% 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 4.7% 3.7% 1.7% 5.2%
2 3.2% 3.0% 1.1% 4.5%
3 3.0% 2.5% 1.3% 3.6%

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 03, 1,469 participants reported to FluWatchers, of which 5% reported symptoms of cough and fever, and 31% of these consulted a healthcare professional. Among participants who reported cough and fever, 90% reported days missed from work or school, resulting in a combined total of 223 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-03
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
1469 5% 31% 90% 223

Influenza Outbreak Surveillance

In week 03, the number of reported laboratory-confirmed outbreaks of influenza decreased compared to the previous week. In week 03, 137 new influenza outbreaks were reported: 78 in long-term care facilities, 14 in hospitals, and 45 in other settings. In addition, one ILI outbreak was reported in a school. Among the 129 outbreaks with influenza type/subtype reported, 52 (40%) were associated with influenza B, and 72 were associated with influenza A, of which 22 were influenza A(H3N2) and 50 influenza A(unsubtyped). Five outbreaks were associated with a mix of influenza A and B.

To date this season, 802 influenza/ILI outbreaks have been reported, of which 471 (59%) occurred in LTC facilities. Among the 696 outbreaks for which the influenza type/subtype was reported, 436 were associated with influenza A (of which 197 were A(H3N2), 238 were A(unsubtyped) and one was A(H1N1)pdm09), 232 were associated with influenza B, and 28 were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 03, the number of cumulative outbreaks reported this season has been greater than during the 2016-17 and 2012-13 seasons, and lower compared to the 2014-15 season.

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-03

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-03
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 69 23
1 12 109 38
2 18 98 48
3 14 78 45

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 03, 182 influenza-associated hospitalizations were reported by participating provinces and territories1. In keeping with the early influenza activity this season, the number of hospitalizations is considerably elevated relative to the same period in the previous two seasons.

To date this season, 2,643 influenza-associated hospitalizations have been reported, 80% of which were associated with influenza A, and 1,814 cases (69%) were in adults 65 years of age or older. To date, 241 ICU admissions and 110 deaths have been reported.

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-03

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 2018-03
Age Group Total
0-4 yr 158
5-19 yr 92
20-44 yr 166
45-64 yr 413
65+ yr 1814
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 03, the number of laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations reported by the Immunization Monitoring Program Active (IMPACT) network increased compared to the previous week. In week 03, 49 hospitaliations were reported, of which 40 (82%) were due to influenza A. The number of weekly hospitalizations has been above the seven-season average since week 45, but following seasonal patterns.

To date this season, 354 pediatric hospitalizations have been reported by the IMPACT network, 250 (71%) of which were associated with influenza A. Fifty-eight ICU admissions and fewer than five deaths have been reported. Compared to the cumulative number of pediatric hospitalizations reported up to week 03 during recent influenza A(H3N2)-dominant seasons, the cumulative number of pediatric hospitalizations reported this season has been greater than the 2016-17 season, but below the 2014-15 and 2012-13 seasons.

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 2018-03

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 2018-03
Age Group Total
0-5 mo 44
6-23 mo 86
2-4 yr 96
5-9 yr 72
10-16 yr 56

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-03

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 2018-03
Report Week 2017-2018 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 8 5 1 13
47 13 4 0 9
48 16 9 2 23
49 23 15 3 28
50 26 23 4 47
51 39 32 4 72
52 61 47 7 92
1 55 40 5 75
2 41 35 4 62
3 49 38 4 67
Figure 8 Footnote 1

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2010-11 to 2017-18

Return to figure 8 note 1 referrer

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 583 influenza viruses [318 A(H3N2), 42 A(H1N1)pdm09 and 223 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition 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 2018-03
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 83 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 1 These A(H3N2) viruses reacted poorly with antisera raised against cell-propagated A/Hong Kong/4801/2014, suggesting some antigenic differences.
Influenza A (H1N1)
A/Michigan/45/2015-like 42 Viruses antigenically similar to A/Michigan/45/2015, the A(H1N1) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine.
Influenza B
B/Brisbane/60/2008-like
(Victoria lineage)
5 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)
6 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)
212 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, 234 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 191 A(H3N2) viruses belonged to genetic group 3C.2a, 42 viruses belonged to subclade 3C.2a1 and one virus belonged to the clade 3C.3a.

Additionally, of the 83 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 60 belonged to genetic group 3C.2a and 11 viruses belonged to subclade 3C.2a1. The virus that showed reduced titer belonged to genetic clade 3C.3a. Sequencing is pending for the remaining 12 virus 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 all six 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 521 influenza viruses for resistance to oseltamivir and 516 viruses for resistance to zanamivir. All but one of the A(H1N1) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-03
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 299 0 (0%) 295 0 (0%)
A (H1N1) 39 1 (2.6%) 39 0 (0%)
B 183 0 (0%) 182 0 (0%)
TOTAL 521 1 (0.2%) 516 0 (0%)

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. For a description of FluWatch surveillance components and definitions, see System Description and Definitions.

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).

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

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