FluWatch report: March 18 to March 24, 2018 (week 12)

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Public Health Agency of Canada

Date published: 2018-03-29

Related Topics
Overall Summary
  • Due to the shortened reporting week, not all data providers were able to report their data.
  • The influenza season peaked in mid-February, but influenza activity remains elevated in many parts of the country.
  • Overall, laboratory detections of influenza are steadily decreasing.
  • 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 12, 13 regions (BC(2), AB(1), ON(7), NB(1) and NS(2)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-12

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 2018-12
Influenza Surveillance Region Activity Level
Newfoundland - Central  No Data
Newfoundland - Eastern  No Data
Grenfell Labrador No Data
Newfoundland - Western  No Data
Prince Edward Island Sporadic
Nova Scotia - Central (Zone 4) Sporadic
Nova Scotia - Western (Zone 1) Localized
Nova Scotia - Northern (Zone 2) Sporadic
Nova Scotia - Eastern (Zone 3) Localized
New Brunswick - Public Health Region 1 Localized
New Brunswick - Public Health Region 2 Sporadic
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 Sporadic
Nord-est Québec No Data
Québec et Chaudieres-Appalaches No Data
Centre-du-Québec No Data
Montréal et Laval No Data
Ouest-du-Québec No Data
Montérégie  No Data
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  No Data
Manitoba - Northern Regional No Data
Manitoba - Prairie Mountain No Data
Manitoba - South No Data
Manitoba - Winnipeg No Data
Saskatchewan - North  Sporadic
Saskatchewan - Central Sporadic
Saskatchewan - South Sporadic
Alberta - North Zone Localized
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 Sporadic
British Columbia - Vancouver Island Localized
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Sporadic
Nunavut - Baffin Sporadic
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 12, the overall percentage of tests positive for influenza was 20%, a decrease from the previous week. Overall, laboratory detections of influenza are steadily decreasing. Influenza B accounted for 53% of influenza detections in week 12.

The percentage of influenza A detections for week 12 is around the average for this time of year. The percentage of tests positive for influenza B in week 12 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 2018-12

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 2018-12
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
11 808 246 73 1387
12 513 182 71 831

To date this season, 58,317 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 92% 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 2018-12

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 2018-12
Reporting
provincesTable Figure 3 - Footnote 1
Week (March 18, 2018 to March 24, 2018) Cumulative (August 27, 2017 to March 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 117 46 55 16 122 2264 458 1390 416 2775 5039
AB 27 12 13 2 90 5532 179 3970 1383 3079 8611
SK 13 3 5 5 53 1677 47 1136 494 1493 3170
MB 5 1 2 2 49 1118 9 373 736 505 1623
ON 148 11 104 33 95 5457 229 3058 2170 4298 9755
QC 331 0 0 331 354 14496 0 0 14496 11579 26075
NB 50 0 0 50 64 1242 11 202 1029 897 2139
NS 27 0 0 27 17 442 0 0 442 226 668
PE 6 1 5 0 4 108 6 102 0 148 256
NL 41 0 0 41 35 323 0 3 320 330 653
YT 5 0 2 3 0 72 7 44 21 42 114
NT 0 0 0 0 1 129 4 125 0 39 168
NU 1 0 1 0 0 43 6 37 0 3 46
Canada 771 74 187 510 884 32903 956 10440 21507 25414 58317
PercentageTable Figure 3 - Footnote 2 47% 10% 24% 66% 53% 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 47,533 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) (58%) and influenza B (47%). 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 (789), 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 2018-12
Age groups (years) Cumulative (August 27, 2017 to March 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 2935 133 537 2265 1379 4314 9%
5-19 2189 120 526 1543 2425 4614 10%
20-44 3992 221 1147 2624 2555 6547 14%
45-64 4346 198 1367 2781 4286 8632 18%
65+ 13831 117 5012 8702 9595 23426 49%
Total 27293 789 8589 17915 20240 47533 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 12, 1.5% of visits to healthcare professionals were due to influenza-like illness (ILI); a slight increase from the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-12

Number of Sentinels Reporting in Week 12: 166

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 2018-12
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 1.3% 2.1% 1.7% 2.7%
12 1.5% 1.8% 1.1% 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 12, 1,345 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 23% of these consulted a healthcare professional. Among participants who reported cough and fever, 72% reported days missed from work or school, resulting in a combined total of 63 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-12
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
1345 3% 23% 72% 63

Influenza Outbreak Surveillance

In week 12, 41 laboratory-confirmed outbreaks of influenza were reported. Among the reported influenza outbreaks, 23 were reported in long-term care facilities (LTC), eight in hospitals, and 10 in other settings. Among the 35 outbreaks with influenza type/subtype reported, 22 (63%) were associated with influenza A, 12 (34%) were associated with influenza B and one outbreak was associated with a mix of influenza A and B (2%).

To date this season, 1,611 influenza/ILI outbreaks have been reported, of which 988 (61%) occurred in LTC facilities. Among the 1,387 outbreaks for which the influenza type/subtype was reported, 758 (55%) were associated with influenza A and 563 (41%) were associated with influenza B, and 66 (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 2018-12

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-12
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 23 10

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,376 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. Among the hospitalizations, 3,067 (70%) were associated with influenza A, and 2,929 cases (67%) were in adults 65 years of age or older.

Additionally, 429 ICU admissions and 218 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 (40%). Adults aged 65 years of age or older accounted the majority of deaths (84%).

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territoriesfigure 6 note 1, weeks 2017-35 to 2018-12

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 2018-12
Age Group Total
0-4 yr 261
5-19 yr 194
20-44 yr 268
45-64 yr 724
65+ yr 2929
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 the preliminary data for week 12, 27 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Influenza A accounted for 63% of the hospitalizations. Pediatric hospitalizations have been on a general decline since week 07.

To date this season, 964 pediatric hospitalizations have been reported by the IMPACT network, 601 (62%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A hospitalizations (40%). Among the 363 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 151 ICU admissions and nine deaths have been reported to date. Children aged 0-23 months accounted for the greatest proportion of ICU cases (29%), followed by children aged 10-16 years (26%). Among the ICU cases with available information, 63% were due to influenza A and approximately 48% 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 2018-12

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 2018-12
Age Group Total
0-5 mo 102
6-23 mo 225
2-4 yr 244
5-9 yr 226
10-16 yr 167

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-12

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 2018-12
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 59 41 18 118
12 27 33 13 89
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 2,710 influenza viruses [1,203 A(H3N2), 182 A(H1N1)pdm09 and 1,325 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 2018-12
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 53 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 182 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)
42 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)
1269 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, 894 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 799 A(H3N2) viruses belonged to genetic group 3C.2a, 93 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 309 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 210 belonged to genetic group 3C.2a and 22 viruses belonged to subclade 3C.2a1. The 53 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the 24 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 37 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the five remaining virus isolates.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 1,041 influenza viruses for resistance to oseltamivir and 1,037 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 2018-12
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 463 0 (0%) 459 0 (0%)
A (H1N1) 131 1 (0.8%) 131 0 (0%)
B 447 0 (0%) 447 1 (0.2%)
TOTAL 1041 1 (0.1%) 1037 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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