FluWatch report: January 21, 2018 to January 27, 2018 (week 4)

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Public Health Agency of Canada

Date published: 2018-02-02

Related Topics
Overall Summary
  • Overall, influenza activity in Canada remains at peak levels but there are signs that activity is starting to slow down in parts of the country.
  • The majority of influenza detections continue to be A(H3N2), although 40% of detections were influenza B in week 04.
  • To date this season, the majority of lab confirmations, hospitalizations and deaths have been among adults 65 years of age and older.
  • A Canadian study reported a mid-season estimate of influenza vaccine effectiveness of 42% overall. The study confirmed an anticipated low vaccine effectiveness of 17% against the A(H3N2) strain and moderate vaccine effectiveness against influenza B of 55%, which is circulating at high levels in Canada this season.
  • 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 04, a similar number of regions reported localized or widespread influenza activity compared to the previous week. Among the 53 regions reporting data for week 04, 6 regions (BC(1), ON(2), QC(3)) reported widespread activity, and 21 regions (BC(1), AB(1), MB(1), ON(5), QC(3), NB(4), NS(3), NL(2), and NT(1)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-04

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 2018-04
Influenza Surveillance Region Activity Level
Newfoundland - Central  Sporadic
Newfoundland - Eastern  Localized
Grenfell Labrador No Activity
Newfoundland - Western  Localized
Prince Edward Island Localized
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 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 Localized
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  Widespread
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 Sporadic
Saskatchewan - South Sporadic
Alberta - North Zone Sporadic
Alberta - Edmonton Sporadic
Alberta - Central Zone  Sporadic
Alberta - Calgary Localized
Alberta - South Zone  Sporadic
British Columbia - Interior Sporadic
British Columbia - Fraser  Widespread
British Columbia - Vancouver Coastal Localized
British Columbia - Vancouver Island Sporadic
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North No Activity
Northwest Territories - South Localized
Nunavut - Baffin No Activity
Nunavut - Kivalliq Sporadic
Nunavut - Kitimeot Sporadic

Laboratory-Confirmed Influenza Detections

In week 04, the overall percentage of tests positive for influenza remained similar to the previous week at 31%. Since week 02, the percentage of tests positive for influenza A has remained stable at 18%. This suggests that the peak for influenza A detections occurred in week 01 (19%). The percentage of tests positive for influenza B remained similar to the previous week.

The percentage of influenza A detections for week 04 is average for this time of year. The percentage of tests positive for influenza B in week 04 continue 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 2018-04

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 2018-04
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 1727 869 79 1914
4 1636 570 52 1640

To date this season, 28,729 laboratory-confirmed influenza detections have been reported, of which 66% 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 2018-04

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 2018-04
Reporting
provincesTable Figure 3 - Footnote 1
Week (January 21, 2018 to January 27, 2018) Cumulative (August 27, 2017 to January 27, 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 169 24 112 33 172 1570 221 958 391 1494 3064
AB 143 6 101 36 140 5004 88 3690 1226 1939 6943
SK 67 2 53 12 69 1300 36 914 350 473 1773
MB 78 0 11 67 25 975 7 327 641 102 1077
ON 428 16 223 189 352 2501 96 1423 982 1780 4281
QC 1241 0 0 1241 800 6540 0 0 6540 3705 10245
NB 0 0 0 0 0 549 0 84 465 125 674
NS 39 0 0 39 13 191 0 0 191 43 234
PE 6 1 5 0 4 53 3 50 0 70 123
NL 11 0 0 11 12 53 0 3 50 31 84
YT 15 1 8 6 2 33 2 19 12 37 70
NT 2 0 2 0 3 116 1 115 0 18 134
NU 3 0 3 0 0 25 0 25 0 2 27
Canada 2202 50 518 1634 1592 18910 454 7608 10848 9819 28729
PercentageTable Figure 3 - Footnote 2 58% 2% 24% 74% 42% 66% 2% 40% 57% 34% 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 25,244 laboratory-confirmed influenza cases (Table 1). Adults 65 years of age and older represent the largest proportion of cases overall (50%), and among cases of influenza A(H3N2) (54%) and influenza B (46%). Adults aged 20-64 represent 33% of cases overall and 31% of influenza A(H3N2) and 36% of influenza B cases. Although much smaller in numbers (402), 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 33% 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 2018-04
Age groups (years) Cumulative (August 27, 2017 to January 27, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 1461 72 505 884 496 1957 8%
5-19 1302 62 550 690 1038 2340 9%
20-44 2690 114 1093 1483 1175 3865 15%
45-64 2761 100 1156 1505 1813 4574 18%
65+ 8715 54 3839 4822 3793 12508 50%
Total 16929 402 7143 9384 8315 25244 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 04, 3% of visits to healthcare professionals were due to influenza-like illness (ILI); a slight increase compared to the previous week, and slightly above the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-04

Number of Sentinels Reporting in Week 04: 140

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 2018-04
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 2.7% 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 4.7% 3.7% 1.7% 5.2%
2 3.2% 3.0% 1.1% 4.5%
3 3.0% 2.5% 1.3% 3.6%
4 3.3% 2.4% 1.7% 3.5%

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 04, 1,479 participants reported to FluWatchers, of which 4% reported symptoms of cough and fever, and 29% of these consulted a healthcare professional. Among participants who reported cough and fever, 73% reported days missed from work or school, resulting in a combined total of 123 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-04
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
1479 4% 29% 73% 123

Influenza Outbreak Surveillance

In week 04, the number of reported laboratory-confirmed outbreaks of influenza decreased compared to the previous week. In week 04, 97 new influenza outbreaks were reported: 60 in long-term care facilities, 13 in hospitals, and 24 in other settings. In addition, six ILI outbreaks were reported schools. Among the 87 outbreaks with influenza type/subtype reported, 39 (45%) were associated with influenza B, and 44 were associated with influenza A. Four outbreaks were associated with a mix of influenza A and B.

To date this season, 916 influenza/ILI outbreaks have been reported, of which 542 (59%) occurred in LTC facilities. Among the 794 outbreaks for which the influenza type/subtype was reported, 483 (61%) were associated with influenza A) and 276 (35%) were associated with influenza B, and 34 (4%) were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 04, the number of cumulative outbreaks reported this season has been greater than during the 2016-17 and 2012-13 seasons, 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 2018-04

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-04
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 60 24

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 04, 130 influenza-associated hospitalizations were reported by participating provinces and territories1. To date this season, 3,018 influenza-associated hospitalizations have been reported, 79% of which were associated with influenza A, and 2,078 cases (69%) were in adults 65 years of age or older. To date, 271 ICU admissions and 120 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 2018-04

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 2018-04
Age Group Total
0-4 yr 176
5-19 yr 113
20-44 yr 185
45-64 yr 466
65+ yr 2078
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 04, 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 04, 88 hospitaliations were reported of which influenza A and B made up almost equal proportion of cases. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 446 pediatric hospitalizations have been reported by the IMPACT network, 299 (67%) of which were associated with influenza A. Children 0-23 months accounted for the largest proportion of influenza A cases (40%) and the smallest propotion of influenza B cases (22%). Among the 147 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (29%).

Additionally, 71 ICU admissions and five deaths have been reported to date. Seventy percent of ICU cases were due to influenza A. Children aged 0-23 months and 10-16 years each accounted for 31% of ICU cases.

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 2018-04

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 2018-04
Age Group Total
0-5 mo 52
6-23 mo 101
2-4 yr 118
5-9 yr 97
10-16 yr 78

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-04

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 2018-04
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 56 40 5 75
2 39 35 4 62
3 49 38 4 67
4 88 35 7 47
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 874 influenza viruses [467 A(H3N2), 51 A(H1N1)pdm09 and 356 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 2018-04
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 118 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 4 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 51 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)
5 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)
10 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)
341 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, 349 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 295 A(H3N2) viruses belonged to genetic group 3C.2a, 53 viruses belonged to subclade 3C.2a1 and one virus belonged to the clade 3C.3a.

Additionally, of the 118 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 75 belonged to genetic group 3C.2a and 12 viruses belonged to subclade 3C.2a1. The four viruses that showed reduced titer belonged to genetic clade 3C.3a. Sequencing is pending for the remaining 27 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 10 viruses had a two amino acid deletion in the HA gene.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 589 influenza viruses for resistance to oseltamivir and 586 viruses for resistance to zanamivir. All but one of the A(H1N1) viruses were sensitive to oseltamivir and all viruses were sensitive to zanamivir (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2018-04
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 324 0 (0%) 321 0 (0%)
A (H1N1) 42 1 (2.4%) 42 0 (0%)
B 223 0 (0%) 223 0 (0%)
TOTAL 589 1 (0.2%) 586 0 (0%)

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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