FluWatch report: February 11 to February 17, 2018 (week 7)

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Public Health Agency of Canada

Date published: 2018-02-23

Related Topics

Overall Summary
  • Overall, influenza activity in Canada remains at peak levels.
  • Influenza activity is decreasing in some parts of the country but at the national level, the decline in activity has been slow.
  • In week 07, 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.
  • The World Health Organization (WHO) has released the recommended composition of the influenza vaccine for use in the 2018-2019 northern hemisphere influenza season. The recommended strain was changed for the A(H3N2) component and one of the influenza B components.
  • 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 07, there was a slight decrease in the number of regions reporting localized or widespread influenza activity compared to the previous week. Among the 53 regions reporting data for week 07, 5 regions (ON(1), QC(4)) reported widespread activity, and 21 regions (BC(2), AB(2), ON(6), QC(1), NB(2), NS(2), NL(3), PE(1) and NU(2)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-07

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 2018-07
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 Sporadic
New Brunswick - Public Health Region 5 Sporadic
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 Widespread
Ouest-du-Québec Widespread
Montérégie  Widespread
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 Sporadic
Saskatchewan - North  Sporadic
Saskatchewan - Central Sporadic
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  Sporadic
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Localized
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Sporadic
Nunavut - Baffin Localized
Nunavut - Kivalliq Localized
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 07, the overall percentage of tests positive for influenza was 33% The percentage of tests positive for influenza A continued to decline slowly. The percentage of tests positive for influenza B continued to increase to 17% in week 07. For the first time this season, detections of influenza B were greater than those of influenza A.

The percentage of influenza A detections for week 07 are below average but remain within the expected range for this time of year. The percentage of tests positive for influenza B in week 07 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 2018-07

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 2018-07
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 1823 502 49 2383
7 1887 305 52 2394

To date this season, 42,773 laboratory-confirmed influenza detections have been reported, of which 60% 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 2018-07

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 2018-07
Reporting
provincesTable Figure 3 - Footnote 1
Week (February 11, 2018 to February 17, 2018) Cumulative (August 27, 2017 to February 17, 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 76 24 43 9 102 1810 296 1166 348 2000 3810
AB 76 8 48 20 167 5281 113 3862 1306 2452 7733
SK 33 1 13 19 88 1558 42 1082 434 898 2456
MB 18 0 3 15 55 1068 7 349 712 217 1285
ON 476 12 154 310 424 3922 138 2154 1630 3093 7015
QC 1,365 0 0 1,365 1,376 10594 0 0 10594 7434 18028
NB 97 4 18 75 70 890 6 165 719 414 1304
NS 27 0 0 27 20 290 0 0 290 112 402
PE 3 0 3 0 13 67 3 64 0 111 178
NL 40 0 0 40 43 160 0 3 157 118 278
YT 3 0 2 1 0 59 5 37 17 39 98
NT 3 2 1 0 1 126 4 122 0 23 149
NU 3 1 2 0 0 35 2 33 0 2 37
Canada 2220 52 287 1881 2359 25860 616 9037 16207 16913 42773
PercentageTable Figure 3 - Footnote 2 48% 2% 13% 85% 52% 60% 2% 35% 63% 40% 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 34,733 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (48%), and among cases of influenza A(H3N2) (54%) and influenza B (44%). Adults aged 20-64 represent 33% of cases overall and 31% of influenza A(H3N2) and 35% of influenza B cases. Although much smaller in numbers (548), 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 53% and 34% 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 2018-07
Age groups (years) Cumulative (August 27, 2017 to February 17, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 2073 106 604 1363 877 2950 8%
5-19 1761 82 652 1027 1845 3606 10%
20-44 3318 151 1266 1901 1807 5125 15%
45-64 3537 137 1401 1999 2778 6315 18%
65+ 10953 72 4600 6281 5784 16737 48%
Total 21642 548 8523 12571 13091 34733 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 07, 4.5% 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 07: 163

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 2018-07
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 3.6% 2.7% 2.1% 3.3%
7 4.5% 2.4% 1.7% 3.0%

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 07, 1,467 participants reported to FluWatchers, of which 4% reported symptoms of cough and fever, and 20% of these consulted a healthcare professional. Among participants who reported cough and fever, 76% reported days missed from work or school, resulting in a combined total of 140 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-07
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
1467 4% 20% 76% 140

Influenza Outbreak Surveillance

In week 07, the number of reported laboratory-confirmed outbreaks of influenza decreased compared to the previous week.In week 07, 94 new influenza outbreaks were reported: 55 in long-term care facilities, 11 in hospitals, and 28 in other settings. In addition, four ILI outbreaks were reported schools. Among the 88 outbreaks with influenza type/subtype reported, 47 (53%) were associated with influenza B, 33 (38%) were associated with influenza A and eight outbreaks were associated with a mix of influenza A and B (9%).

To date this season, 1,228 influenza/ILI outbreaks have been reported, of which 729 (60%) occurred in LTC facilities. Among the 1,070 outbreaks for which the influenza type/subtype was reported, 601 (56%) were associated with influenza A and 415 (39%) were associated with influenza B, and 54 (5%) were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 07, 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 2018-07

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-07
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

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 07, 46 influenza-associated hospitalizations were reported by participating provinces and territories1.  To date this season, 3,451 influenza-associated hospitalizations have been reported, 77% of which were associated with influenza A, and 2,357 cases (68%) were in adults 65 years of age or older. To date, 317 ICU admissions and 163 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 2018-07

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 2018-07
Age Group Total
0-4 yr 200
5-19 yr 131
20-44 yr 212
45-64 yr 551
65+ yr 2357
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 07, 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 07, 89 hospitalizations were reported of which 52 (60%) were due to influenza A. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 686 pediatric hospitalizations have been reported by the IMPACT network, 431 (63%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 255 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (30%).

Additionally, 114 ICU admissions and six deaths have been reported to date. Children aged 0-23 months and 10-16 years each accounted for 27% of ICU cases. Among the ICU cases with available information, 65% were due to influenza A and approximately 43% had no reported previous or concurrent medical conditions.

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 2018-07

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 2018-07
Age Group Total
0-5 mo 74
6-23 mo 156
2-4 yr 179
5-9 yr 159
10-16 yr 118

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-07

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 2018-07
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 79 38 15 79
7 89 40 17 120
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 1,701 influenza viruses [895 A(H3N2), 86 A(H1N1)pdm09 and 720 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 2018-07
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 166 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 18 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 86 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)
7 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)
24 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)
689 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, 711 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 632 A(H3N2) viruses belonged to genetic group 3C.2a, 77 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 184 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 144 belonged to genetic group 3C.2a and 16 viruses belonged to subclade 3C.2a1. The 18 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the six 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 22 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 790 influenza viruses for resistance to oseltamivir and 786 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 2018-07
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 401 0 (0%) 397 0 (0%)
A (H1N1) 67 1 (1.5%) 67 0 (0%)
B 322 0 (0%) 322 1 (0.3%)
TOTAL 790 1 (0.1%) 786 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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