FluWatch report: February 18 to February 24, 2018 (week 8)

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Public Health Agency of Canada

Date published: 2018-03-02

Related Topics
Overall Summary
  • Overall, influenza activity in Canada remains at peak levels.
  • Influenza activity is slowly decreasing in many parts of the country.
  • Detections of influenza B were greater than those of influenza A.
  • 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 08, three regions (BC(1), ON(1), and QC(1)) reported widespread activity, and 25 regions (BC(1), AB(2), SK(1), MB(1), ON(6), QC(5), NB(3), NS(3), and NL(3) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-08

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 2018-08
Influenza Surveillance Region Activity Level
Newfoundland - Central  Localized
Newfoundland - Eastern  Localized
Grenfell Labrador No Activity
Newfoundland - Western  Localized
Prince Edward Island Sporadic
Nova Scotia - Central (Zone 4) Localized
Nova Scotia - Western (Zone 1) Localized
Nova Scotia - Northern (Zone 2) Sporadic
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 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 Localized
Centre-du-Québec Widespread
Montréal et Laval Localized
Ouest-du-Québec Localized
Montérégie  Localized
Ontario - Central East Widespread
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 Sporadic
Manitoba - South Sporadic
Manitoba - Winnipeg Localized
Saskatchewan - North  Sporadic
Saskatchewan - Central Localized
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Localized
Alberta - Central Zone  Sporadic
Alberta - Calgary Localized
Alberta - South Zone  Sporadic
British Columbia - Interior Localized
British Columbia - Fraser  Widespread
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Sporadic
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North No Data
Northwest Territories - South No Data
Nunavut - Baffin Sporadic
Nunavut - Kivalliq Sporadic
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 08, the overall percentage of tests positive for influenza was 31%, a small decrease from the previous week. The percentage of tests positive for influenza A continues to decline slowly to 14% in week 08. The percentage of tests positive for influenza B was similar to the previous week (17%). Similar to the previous week, detections of influenza B were greater than those of influenza A.

The percentage of influenza A detections for week 08 are below average but remain within the expected range for this time of year. The percentage of tests positive for influenza B in week 08 continues 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 2018-08

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 2018-08
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 808 49 1730
3 1649 870 80 1912
4 1675 632 57 1802
5 1664 542 54 2125
6 1819 506 49 2383
7 1773 392 62 2443
8 1662 239 43 2295

To date this season, 44,497 laboratory-confirmed influenza detections have been reported, of which 59% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 93% 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 2018-08

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 2018-08
Reporting
provincesTable Figure 3 - Footnote 1
Week (February 18, 2018 to February 24, 2018) Cumulative (August 27, 2017 to February 24, 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 57 20 33 4 141 1872 316 1199 357 2141 4013
AB 43 11 24 8 139 5330 124 3888 1318 2603 7933
SK 0 0 0 0 0 28 1 18 9 7 35
MB 15 0 2 13 63 1083 7 357 719 280 1363
ON 440 9 159 272 359 4343 157 2396 1790 3454 7797
QC 1 237 0 0 1 237 1 290 11827 0 0 11827 8756 20583
NB 71 0 0 71 110 961 6 165 790 524 1485
NS 16 0 0 16 22 306 0 0 306 134 440
PE 2 0 2 0 8 69 3 66 0 119 188
NL 36 0 0 36 48 196 0 3 193 166 362
YT 2 0 2 0 1 61 5 39 17 40 101
NT 1 0 1 0 2 127 4 123 0 28 155
NU 4 3 1 0 1 39 5 34 0 3 42
Canada 1924 43 224 1657 2184 26242 628 8288 17326 18255 44497
PercentageTable Figure 3 - Footnote 2 47% 2% 12% 86% 53% 59% 2% 32% 66% 41% 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 38,578 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 30% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (555), the majority of influenza A(H1N1) cases are among adults less than 65 years of age, with adults aged 20-64 and children 0-19 years accounting for 54% and 32% of cases respectively.

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 2018-08
Age groups (years) Cumulative (August 27, 2017 to February 24, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 2351 99 488 1764 1059 3410 9%
5-19 1819 79 488 1252 1974 3793 10%
20-44 3394 157 1061 2176 2000 5394 14%
45-64 3724 143 1251 2330 3252 6976 18%
65+ 11828 77 4413 7338 7177 19005 49%
Total 23116 555 7701 14860 15462 38578 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 08, 3.0% of visits to healthcare professionals were due to influenza-like illness (ILI); an increase compared to the previous week, and above the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-06

Number of Sentinels Reporting in Week 08: 164

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 2018-08
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 2.8% 2.5% 1.3% 3.6%
4 3.1% 2.4% 1.7% 3.5%
5 4.1% 2.7% 2.0% 4.4%
6 3.5% 2.7% 2.1% 3.3%
7 3.6% 2.4% 1.7% 3.0%
8 3.0% 2.3% 1.9% 2.7%

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 08, 1,419 participants reported to FluWatchers, of which 4% reported symptoms of cough and fever, and 30% of these consulted a healthcare professional. Among participants who reported cough and fever, 78% reported days missed from work or school, resulting in a combined total of 112 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-08
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
1419 4% 30% 78% 112

Influenza Outbreak Surveillance

In week 08, the number of reported laboratory-confirmed outbreaks of influenza decreased compared to the previous week. In week 08, 86 new influenza outbreaks were reported: 56 in long-term care facilities, eight in hospitals, and 22 in other settings. In addition, three ILI outbreaks were reported schools. Among the 75 outbreaks with influenza type/subtype reported, 35 (47%) were associated with influenza B, 34 (45%) were associated with influenza A and six outbreaks were associated with a mix of influenza A and B (8%).

To date this season, 1,317 influenza/ILI outbreaks have been reported, of which 785 (60%) occurred in LTC facilities. Among the 1,145 outbreaks for which the influenza type/subtype was reported, 635 (55%) were associated with influenza A and 450 (39%) were associated with influenza B, and 60 (5%) were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 08, the number of cumulative outbreaks reported this season has been greater than during the 2016-17 season 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 2018-08

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-08
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 63 24
5 9 54 19
6 10 75 31
7 11 55 28
8 8 56 22

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 3,584 influenza-associated hospitalizations were reported by participating provinces and territories1. Among the hospitalizations, 2,702 (75%) were associated with influenza A, and 2,434 cases (68%) were in adults 65 years of age or older.

Additionally, 339 ICU admissions and 170 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (43%), followed closely by adults aged 20-64 (41%). Adults aged 65 years of age or older accounted the majority of deaths (82%).

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-08

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 2018-08
Age Group Total
0-4 yr 206
5-19 yr 142
20-44 yr 219
45-64 yr 583
65+ yr 2434
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 08, the number of laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations reported by the Immunization Monitoring Program Active (IMPACT) network decreased compared to the previous week. In week 08, 68 hospitalizations were reported of which 48 (70%) were due to influenza A. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 756 pediatric hospitalizations have been reported by the IMPACT network, 481 (64%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 275 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (30%).

Additionally, 126 ICU admissions and eight deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (29%). Among the ICU cases with available information, 66% were due to influenza A and approximately 43% had no reported previous or concurrent medical conditions. All 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 2018-08

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 2018-08
Age Group Total
0-5 mo 82
6-23 mo 170
2-4 yr 199
5-9 yr 170
10-16 yr 135

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-08

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 2018-08
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 60 47 7 92
1 57 40 5 75
2 39 35 4 62
3 50 38 4 67
4 93 35 7 47
5 67 40 11 59
6 78 38 15 79
7 88 40 17 120
8 68 47 25 139
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 1,917 influenza viruses [981 A(H3N2), 98 A(H1N1)pdm09 and 838 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 2018-08
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 189 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 29 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 98 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) 8 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)
28 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)
802 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, 763 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 679 A(H3N2) viruses belonged to genetic group 3C.2a, 82 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 218 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 153 belonged to genetic group 3C.2a and 17 viruses belonged to subclade 3C.2a1. The 29 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the 19 remaining 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 28 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the two remaining virus isolates.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 852 influenza viruses for resistance to oseltamivir and 848 viruses for resistance to zanamivir. All but one of the A(H1N1) viruses 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 2018-08
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 419 0 (0%) 415 0 (0%)
A (H1N1) 78 1 (1.3%) 78 0 (0%)
B 355 0 (0%) 355 1 (0.3%)
TOTAL 852 1 (0.1%) 848 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. 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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