FluWatch report:  March 4, 2018 to March 10, 2018 (week 10)

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Public Health Agency of Canada

Date published: 2018-03-16

Related Topics
Overall Summary
  • All indicators of influenza activity decreased from the previous week.
  • Influenza activity remains elevated 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 10, two regions (BC(1), and QC(1)) reported widespread activity, and 24 regions (BC(2), AB(2), ON(6), QC(4), NB(2), NS(4), NL(3), and NT(1)) reported localized activity.

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2018-10

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 2018-10
Influenza Surveillance Region Activity Level
Newfoundland - Central  Localized
Newfoundland - Eastern  Localized
Grenfell Labrador Sporadic
Newfoundland - Western  Localized
Prince Edward Island Sporadic
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 Sporadic
New Brunswick - Public Health Region 6 Sporadic
New Brunswick - Public Health Region 7 Sporadic
Nord-est Québec Localized
Québec et Chaudieres-Appalaches Localized
Centre-du-Québec Localized
Montréal et Laval Widespread
Ouest-du-Québec Localized
Montérégie  Sporadic
Ontario - Central East Localized
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  No Activity
Manitoba - Northern Regional Sporadic
Manitoba - Prairie Mountain Sporadic
Manitoba - South No Activity
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 Sporadic
Alberta - South Zone  Localized
British Columbia - Interior Sporadic
British Columbia - Fraser  Widespread
British Columbia - Vancouver Coastal Localized
British Columbia - Vancouver Island Localized
British Columbia - Northern Sporadic
Yukon No Activity
Northwest Territories - North Localized
Northwest Territories - South Sporadic
Nunavut - Baffin Sporadic
Nunavut - Kivalliq Sporadic
Nunavut - Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 10, the overall percentage of tests positive for influenza was 27%. The overall percentage of tests positive for influenza has been slowly decreasing from the peak in week 07. Detections of influenza B continue to be greater than those of influenza A. Influenza B accounted for 55% of influenza detections in week 10.

The percentage of influenza A detections for week 10 are below average but remain within the expected range for this time of year. The percentage of tests positive for influenza B in week 10 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 2018-10

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 2018-10
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 1462 326 51 2058
10 1001 258 75 1669

To date this season, 53,898 laboratory-confirmed influenza detections have been reported, of which 57% 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 2018-10

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 2018-10
Reporting
provincesTable Figure 3 - Footnote 1
Week (March 4, 2018 to March 10, 2018) Cumulative (August 27, 2017 to March 10, 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 130 36 73 21 160 2102 375 1310 417 2497 4599
AB 58 17 21 20 110 5452 152 3936 1364 2872 8324
SK 27 0 8 19 80 1625 43 1109 473 1174 2799
MB 9 0 3 6 43 1106 7 369 730 396 1502
ON 225 16 128 81 194 4970 196 2777 1997 3979 8949
QC 729 0 0 729 868 13627 0 0 13627 10658 24285
NB 93 5 16 72 97 1122 11 202 909 705 1827
NS 37 0 0 37 22 386 0 0 386 172 558
PE 6 0 6 0 11 87 3 84 0 135 222
NL 23 0 0 23 40 256 0 3 253 265 521
YT 2 1 1 0 0 65 7 40 18 41 106
NT 0 0 0 0 2 129 4 125 0 32 161
NU 0 0 0 0 0 42 6 36 0 3 45
Canada 1339 75 256 1008 1627 30969 804 9991 20174 22929 53898
PercentageTable Figure 3 - Footnote 2 45% 6% 19% 75% 55% 57% 3% 32% 65% 43% 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 44,153 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 (659), 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 2018-10
Age groups (years) Cumulative (August 27, 2017 to March 10, 2018)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 2741 118 524 2099 1252 3993 9%
5-19 2068 93 512 1463 2259 4327 10%
20-44 3760 188 1110 2462 2351 6111 14%
45-64 4093 167 1322 2604 3883 7976 18%
65+ 13092 93 4792 8207 8654 21746 49%
Total 25754 659 8260 16835 18399 44153 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 10, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI); a decrease from the previous week.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2018-10

Number of Sentinels Reporting in Week 10: 170

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 2018-10
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 1.8% 2.1% 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 10, 1,385 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 22% 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 74 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2018-10
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
1385 3% 22% 73% 74

Influenza Outbreak Surveillance

In week 10, 64 laboratory-confirmed outbreaks of influenza were reported, a sharp decrease compared to the previous week. Among the reported influenza outbreaks, 42 were reported in long-term care facilities(LTC), 12 in hospitals, and 10 in other settings. In addition, six ILI outbreaks were reported schools. Among the 52 outbreaks with influenza type/subtype reported, 29 (56%) were associated with influenza A, 23 (44%) were associated with influenza B.

To date this season, 1,508 influenza/ILI outbreaks have been reported, of which 917 (61%) occurred in LTC facilities. Among the 1,294 outbreaks for which the influenza type/subtype was reported, 678 (52%) were associated with influenza A and 500 (39%) were associated with influenza B, and 64 (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 2018-10

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2018-10
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 59 22
9 8 79 16
10 12 42 10

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season, 4,086 influenza-associated hospitalizations were reported by participating provinces and territories. Among the hospitalizations, 2,936 (72%) were associated with influenza A, and 2,750 cases (67%) were in adults 65 years of age or older.

Additionally, 394 ICU admissions and 201 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 (41%). 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 2018-10

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 2018-10
Age Group Total
0-4 yr 240
5-19 yr 172
20-44 yr 249
45-64 yr 675
65+ yr 2750
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 10, 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 10, 57 hospitalizations were reported of which 33 (58%) were due to influenza A. Pediatric hospitalizations have been decreasing since week 07. The number of weekly hospitalizations has been above the seven-season average since week 45.

To date this season, 882 pediatric hospitalizations have been reported by the IMPACT network, 555 (63%) of which were associated with influenza A. Children 0-23 months  accounted for the largest proportion of influenza A hospitalizations (40%). Among the 327 hospitalizations due to influenza B, children 5-9 years accounted for the largest proportion of cases (31%).

Additionally, 139 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 42% 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 2018-10

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 2018-10
Age Group Total
0-5 mo 96
6-23 mo 202
2-4 yr 230
5-9 yr 203
10-16 yr 151

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2018-10

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 2018-10
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 26 23 4 47
51 39 32 4 72
52 62 47 7 92
1 57 40 5 75
2 39 35 4 62
3 52 38 4 67
4 93 35 7 47
5 70 40 11 59
6 74 38 15 79
7 89 40 17 120
8 72 47 25 139
9 69 50 13 153
10 57 48 17 135
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 2,367 influenza viruses [1,139 A(H3N2), 155 A(H1N1)pdm09 and 1,073 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 2018-10
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 226 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 45 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 155 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) 10 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)
37 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)
1026 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, 868 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 779 A(H3N2) viruses belonged to genetic group 3C.2a, 87 viruses belonged to subclade 3C.2a1 and two viruses belonged to the clade 3C.3a.

Additionally, of the 271 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 196 belonged to genetic group 3C.2a and 21 viruses belonged to subclade 3C.2a1. The 45 viruses that showed reduced titer to A/Hong Kong/4801/2014 belonged to genetic clade 3C.3a. Sequencing is pending for the nine 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 36 viruses had a two amino acid deletion in the HA gene. Sequencing is pending for the one remaining virus isolate.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 989 influenza viruses for resistance to oseltamivir and 985 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 2018-10
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 454 0 (0%) 450 0 (0%)
A (H1N1) 113 1 (0.9%) 113 0 (0%)
B 422 0 (0%) 422 1 (0.2%)
TOTAL 989 1 (0.1%) 985 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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