FluWatch report: February 25 to March 3, 2018 (week 9)

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Public Health Agency of Canada

Date published: 2018-03-09

Related Topics
Overall Summary
  • Laboratory data suggests that the influenza season peaked in week 07 but influenza activity in Canada remains high .
  • Influenza activity is slowly decreasing in many parts of the country.
  • Detections of influenza B continue to be 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 09, seven regions (BC(2), ON(1), and QC(4)) reported widespread activity, and 22 regions (BC(1), AB(1), MB(2), ON(5), QC(2), NB(3), NS(4), NL(3), and PE(1)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-09

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 2018-09
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) 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 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 Widespread
Québec et Chaudieres-Appalaches Widespread
Centre-du-Québec Widespread
Montréal et Laval Localized
Ouest-du-Québec Widespread
Montérégie  Localized
Ontario - Central East Widespread
Ontario - Central West Localized
Ontario - Eastern Localized
Ontario - North East Localized
Ontario - North West  Sporadic
Ontario - South West  Localized
Ontario - Toronto Localized
Manitoba - Interlake-Eastern  Sporadic
Manitoba - Northern Regional No Activity
Manitoba - Prairie Mountain Localized
Manitoba - South Sporadic
Manitoba - Winnipeg Localized
Saskatchewan - North  Sporadic
Saskatchewan - Central Sporadic
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Localized
Alberta - Central Zone  Sporadic
Alberta - Calgary Sporadic
Alberta - South Zone  Sporadic
British Columbia - Interior Sporadic
British Columbia - Fraser  Widespread
British Columbia - Vancouver Coastal Localized
British Columbia - Vancouver Island Widespread
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South No Activity
Nunavut - Baffin Sporadic
Nunavut - Kivalliq Sporadic
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 09, the overall percentage of tests positive for influenza was 30%. For the past two weeks, the percentage of tests positive for influenza B has decreased. This indicates that the peak for influenza B detections occurred in week 07. This also suggests that the peak for the influenza season occurred week 07.

The percentage of influenza A detections for week 09 are below average but remain within the expected range for this time of year. The percentage of tests positive for influenza B in week 09 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 2018-09

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 2018-09
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 1644 277 51 2354
9 1412 323 48 1991

To date this season, 50,912 laboratory-confirmed influenza detections have been reported, of which 58% 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 2018-09

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 2018-09
Reporting
provincesTable Figure 3 - Footnote 1
Week (February 25, 2018 to March 3, 2018) Cumulative (August 27, 2017 to March 3, 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 25 11 14 0 22 1968 339 1237 392 2337 4305
AB 463 13 318 132 122 5393 134 3915 1344 2749 8142
SK 27 0 8 19 80 1625 43 1109 473 1174 2799
MB 25 2 22 1 1 1097 7 365 725 353 1450
ON 44 4 27 13 20 4697 178 2646 1873 3732 8429
QC 80 0 0 80 22 12892 0 0 12892 9790 22682
NB 11 0 3 8 0 1029 6 186 837 608 1637
NS 2 0 0 2 0 349 0 0 349 150 499
PE 1 0 1 0 0 81 3 78 0 124 205
NL 0 0 0 0 0 233 0 3 230 225 458
YT 0 0 0 0 2 63 6 39 18 41 104
NT 0 0 0 0 0 128 4 124 0 29 157
NU 5 0 5 0 0 42 6 36 0 3 45
Canada 683 30 398 255 269 29597 726 9738 19133 21315 50912
PercentageTable Figure 3 - Footnote 2 72% 4% 58% 37% 28% 58% 2% 33% 65% 42% 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 41,767 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 30% of influenza A(H3N2) and 34% of influenza B cases. Although much smaller in numbers (596), 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 2018-09
Age groups (years) Cumulative (August 27, 2017 to March 3, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 2569 106 507 1956 1159 3728 9%
5-19 1971 87 499 1385 2135 4106 10%
20-44 3610 170 1086 2354 2229 5839 14%
45-64 3926 150 1286 2490 3596 7522 18%
65+ 12593 83 4615 7895 7979 20572 49%
Total 24669 596 7993 16080 17098 41767 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 09, 3.2% of visits to healthcare professionals were due to influenza-like illness (ILI); similar 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 2018-09

Number of Sentinels Reporting in Week 09: 177

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 2018-09
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 3.4% 2.4% 1.7% 3.0%
8 3.2% 2.3% 1.9% 2.7%
9 3.2% 2.2% 1.8% 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 09, 1,419 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 14% of these consulted a healthcare professional. Among participants who reported cough and fever, 69% reported days missed from work or school, resulting in a combined total of 90 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-09
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 3% 14% 69% 90

Influenza Outbreak Surveillance

In week 09, 103 laboratory-confirmed outbreaks of influenza were reported, an increase compared to the previous week. Among the reported influenza outbreaks, 79 were reported in long-term care facilities, eight in hospitals, and 16 in other settings. In addition, seven ILI outbreaks were reported schools. Among the 87 outbreaks with influenza type/subtype reported, 48 (55%) were associated with influenza B, 37 (43%) were associated with influenza A and two outbreaks were associated with a mix of influenza A and B (2%).

To date this season, 1,428 influenza/ILI outbreaks have been reported, of which 865 (61%) occurred in LTC facilities. Among the 1,232 outbreaks for which the influenza type/subtype was reported, 672 (54%) were associated with influenza A and 498 (40%) were associated with influenza B, and 62 (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 2018-09

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-09
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 57 22
9 8 79 16

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 3,892 influenza-associated hospitalizations were reported by participating provinces and territories1. Among the hospitalizations, 2,861 (74%) were associated with influenza A, and 2,629 cases (68%) were in adults 65 years of age or older.

Additionally, 377 ICU admissions and 189 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 (42%). 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 2018-09

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 2018-09
Age Group Total
0-4 yr 227
5-19 yr 164
20-44 yr 236
45-64 yr 636
65+ yr 2629
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 09, 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 09, 58 hospitalizations were reported of which 36 (62%) were due to influenza A. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 811 pediatric hospitalizations have been reported by the IMPACT network, 516 (64%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (39%). Among the 295 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (30%).

Additionally, 135 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 closely by children aged 10-16 years (27%). Among the ICU cases with available information, 65% 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 2018-09

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 2018-09
Age Group Total
0-5 mo 90
6-23 mo 184
2-4 yr 214
5-9 yr 182
10-16 yr 141

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-09

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 2018-09
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 88 40 17 120
7 88 40 17 120
8 69 47 25 139
9 58 50 13 153
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 2,085 influenza viruses [1,040 A(H3N2), 123 A(H1N1)pdm09 and 922 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 2018-09
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 207 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 30 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 123 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)
36 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)
878 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, 803 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 719 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 237 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 176 belonged to genetic group 3C.2a and 21 viruses belonged to subclade 3C.2a1. The 30 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the 10 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 28 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the eight remaining virus isolates.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 913 influenza viruses for resistance to oseltamivir and 909 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 2018-09
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 435 0 (0%) 431 0 (0%)
A (H1N1) 89 1 (1.1%) 89 0 (0%)
B 389 0 (0%) 389 1 (0.3%)
TOTAL 913 1 (0.1%) 909 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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