FluWatch report: March 25 to March 31, 2018 (week 13)

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Public Health Agency of Canada

Date published: 2018-04-06

Related Topics
Overall Summary
  • The influenza season peaked in mid-February, but influenza activity remains elevated in many parts of the country.
  • Laboratory detections of influenza are steadily decreasing.
  • Weekly pediatric hospitalizations have been on a general decline since mid-February.
  • 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 13, two regions (BC(1) and QC(1)) reported widespread activity and 23 regions (BC(2), SK(1), ON(7), QC(3), NB(3), NL(2), PE(1) and NS(4)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-13

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 2018-13
Influenza Surveillance Region Activity Level
Newfoundland - Central  Localized
Newfoundland - Eastern  Localized
Grenfell Labrador No Activity
Newfoundland - Western  Sporadic
Prince Edward Island Localized
Nova Scotia - Central (Zone 4) Localized
Nova Scotia - Western (Zone 1) Localized
Nova Scotia - Northern (Zone 2) Localized
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 Sporadic
New Brunswick - Public Health Region 4 Sporadic
New Brunswick - Public Health Region 5 No Activity
New Brunswick - Public Health Region 6 Sporadic
New Brunswick - Public Health Region 7 Localized
Nord-est Québec Localized
Québec et Chaudieres-Appalaches Sporadic
Centre-du-Québec Widespread
Montréal et Laval Sporadic
Ouest-du-Québec Localized
Montérégie  Localized
Ontario - Central East Localized
Ontario - Central West Localized
Ontario - Eastern Localized
Ontario - North East Localized
Ontario - North West  Localized
Ontario - South West  Localized
Ontario - Toronto Localized
Manitoba - Interlake-Eastern  Sporadic
Manitoba - Northern Regional Sporadic
Manitoba - Prairie Mountain Sporadic
Manitoba - South Sporadic
Manitoba - Winnipeg Sporadic
Saskatchewan - North  Sporadic
Saskatchewan - Central Sporadic
Saskatchewan - South Localized
Alberta - North Zone Sporadic
Alberta - Edmonton Sporadic
Alberta - Central Zone  Sporadic
Alberta - Calgary Sporadic
Alberta - South Zone  Sporadic
British Columbia - Interior Sporadic
British Columbia - Fraser  Localized
British Columbia - Vancouver Coastal Widespread
British Columbia - Vancouver Island Localized
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Sporadic
Nunavut - Baffin No Data
Nunavut - Kivalliq No Data
Nunavut - Kitimeot No Data

Laboratory-Confirmed Influenza Detections

In week 13, the overall percentage of tests positive for influenza was 19%, a decrease from the previous week. Overall, laboratory detections of influenza are steadily decreasing. Influenza B accounted for 54% of influenza detections in week 13.

The percentage of influenza A detections for week 13 is around the average for this time of year. The percentage of tests positive for influenza B in week 13 is above average but within the expected range 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 2018-13

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 2018-13
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 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
13 431 176 35 739

To date this season, 59,699 laboratory-confirmed influenza detections have been reported, of which 56% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 91% of subtyped influenza A detections. For more detailed weekly and cumulative influenza data, see the text descriptions for Figures 2 and 3 or the Respiratory Virus Detections in Canada Report.

Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, weeks 2017-35 to 2018-13

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 2018-13
Reporting
provincesTable Figure 3 - Footnote 1
Week (March 25, 2018 to March 31, 2018) Cumulative (August 27, 2017 to March 31, 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 61 12 41 8 85 2321 471 1431 419 2860 5181
AB 24 12 5 7 63 5557 191 3976 1390 3150 8707
SK 13 3 5 5 53 1677 47 1136 494 1493 3170
MB 2 0 1 1 37 1120 9 374 737 542 1662
ON 163 7 99 57 114 5665 237 3157 2271 4446 10111
QC 226 0 0 226 264 14722 0 0 14722 11843 26565
NB 66 2 5 59 48 1308 13 207 1088 945 2253
NS 33 0 0 33 31 475 0 0 475 257 732
PE 15 0 14 1 6 123 6 116 1 154 277
NL 27 0 0 27 25 350 0 3 347 355 705
YT 0 0 0 0 0 72 7 44 21 42 114
NT 0 0 0 0 4 129 4 125 0 44 173
NU 2 0 2 0 0 46 6 40 0 3 49
Canada 632 36 172 424 730 33565 991 10609 21965 26134 59699
PercentageTable Figure 3 - Footnote 2 46% 6% 27% 67% 54% 56% 3% 32% 65% 44% 100%
Table Figure 3 - Footnote 1

Specimens from NT, YT, and NU are sent to reference laboratories in other provinces.

Return to Table Figure 3 - Footnote 1 referrer

Table Figure 3 - Footnote 2

Percentage of tests positive for sub-types of influenza A are a percentage of all influenza A detections.

Return to Table Figure 3 - Footnote 2 referrer

Table Figure 3 - Footnote 3

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Return to first Table Figure 3 - Footnote 3 referrer

Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Cumulative data includes updates to previous weeks.

To date this season, detailed information on age and type/subtype has been received for 48,582 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) (59%) and influenza B (48%). Adults aged 20-64 represent 32% of cases overall and 29% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (814), 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 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 2018-13
Age groups (years) Cumulative (August 27, 2017 to March 31, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 2991 136 544 2311 1406 4397 9%
5-19 2216 121 532 1563 2474 4690 10%
20-44 4048 227 1164 2657 2613 6661 14%
45-64 4426 207 1395 2824 4413 8839 18%
65+ 14100 123 5135 8842 9895 23995 49%
Total 27781 814 8770 18197 20801 48582 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 Practitioners Sentinel Syndromic Surveillance

In week 13, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI); an increase from the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-13

Number of Sentinels Reporting in Week 13: 172

Figure 4

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 2018-13
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 3.0% 2.3% 1.9% 2.7%
9 2.8% 2.2% 1.8% 2.7%
10 1.7% 2.1% 1.8% 2.7%
11 1.2% 2.1% 1.7% 2.7%
12 1.6% 1.8% 1.1% 2.7%
13 1.8% 1.7% 1.2% 2.6%

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 13, 1,287 participants reported to FluWatchers, of which 2% reported symptoms of cough and fever, and 16% 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 44 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-13
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
1287 2% 16% 76% 44

Influenza Outbreak Surveillance

In week 13, 42 laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, 29 were reported in long-term care facilities (LTC), five in hospitals, and eight in other settings. Among the 32 outbreaks with influenza type/subtype reported, 18 (56%) were associated with influenza A, 13 (41%) were associated with influenza B and one outbreak was associated with a mix of influenza A and B (3%).

To date this season, 1,663 influenza/ILI outbreaks have been reported, of which 1,025 (62%) occurred in LTC facilities. Among the 1,427 outbreaks for which the influenza type/subtype was reported, 781 (55%) were associated with influenza A and 579 (41%) were associated with influenza B, and 67 (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 2018-13

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-13
Report week Hospitals Long Term Care Facilities Other
35 0 0 0
36 0 1 0
37 0 0 0
38 0 2 0
39 0 1 1
40 1 0 0
41 0 0 1
42 0 2 1
43 3 1 1
44 0 1 0
45 3 1 4
46 0 2 5
47 0 2 5
48 9 11 7
49 4 14 12
50 9 31 16
51 11 48 28
52 5 72 23
1 12 110 38
2 18 99 48
3 14 84 45
4 13 65 24
5 9 55 19
6 10 77 31
7 11 58 28
8 8 60 22
9 8 83 16
10 12 42 10
11 2 43 12
12 8 31 10
13 5 29 8

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,500 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. Among the hospitalizations, 3,116 (69%) were associated with influenza A, and 2,990 cases (66%) were in adults 65 years of age or older.

Additionally, 439 ICU admissions and 230 deaths have been reported to date. Adults aged 65 years of age or older accounted for the greatest proportion of ICU cases (44%), followed closely by adults aged 20-64 (40%). Adults aged 65 years of age or older accounted the majority of deaths (83%).

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-13

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 2018-13
Age Group Total
0-4 yr 266
5-19 yr 203
20-44 yr 286
45-64 yr 755
65+ yr 2990
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 13, 26 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 62% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07.

To date this season, 995 pediatric hospitalizations have been reported by the IMPACT network, 619 (62%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A hospitalizations (41%). Among the 376 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 159 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (28%), followed by children aged 10-16 years (26%). Among the ICU cases with available information, 64% were due to influenza A and approximately 48% had no reported previous or concurrent medical conditions. All but one reported deaths were among children over the age of two.

Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, weeks 2017-35 to 2018-13

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 2018-13
Age Group Total
0-5 mo 108
6-23 mo 234
2-4 yr 251
5-9 yr 232
10-16 yr 170

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-13

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 2018-13
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 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 62 47 7 92
1 57 40 5 75
2 38 35 4 62
3 52 38 4 67
4 94 35 7 47
5 70 40 11 59
6 74 38 15 79
7 89 40 17 120
8 72 47 25 139
9 68 50 13 153
10 58 48 17 135
11 57 41 18 118
12 35 33 13 89
13 26 32 14 67
Figure 8 Footnote 1

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

Return to figure 8 note 1 referrer

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 2,856 influenza viruses [1,287 A(H3N2), 200 A(H1N1)pdm09 and 1,369 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition (HI) assay during the 2017-18 season, most viruses were antigenically similar to the cell-culture propagated reference strains recommended by WHO.

Table 3 - Influenza antigenic strain characterizations, Canada, weeks 2017-35 to 2018-13
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 256 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 65 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 200 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) 14 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)
43 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)
1312 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, 965 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 862 A(H3N2) viruses belonged to genetic group 3C.2a, 101 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 322 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 232 belonged to genetic group 3C.2a and 24 viruses belonged to subclade 3C.2a1. The 65 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the remaining one isolate.

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 43 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the remaining virus isolate.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,103 influenza viruses for resistance to oseltamivir and 1,099 viruses for resistance to zanamivir. All but one of the A(H1N1)pdm 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 2018-13
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 474 0 (0%) 471 0 (0%)
A (H1N1) 143 1 (0.7%) 143 0 (0%)
B 486 0 (0%) 485 1 (0.2%)
TOTAL 1103 1 (0.1%) 1099 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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