FluWatch report: FluWatch report: December 10, 2017 to December 16, 2017 (week 50)

Overall Summary
  • Overall, influenza activity continues to increase across Canada. Some indicators increased slightly compared to the previous week; however, there was a notable increase in the number of outbreaks and hospitalizations reported in week 50.
  • The majority of influenza detections continue to be A(H3N2), although a substantially greater number of influenza B detections has also been reported compared to previous seasons.
  • In keeping with the early influenza activity this season, several indicators of influenza activity are above the expected levels for this time of year.
  • The majority of lab confirmations, hospitalizations and deaths have been among adults 65 years of age and older.
  • Since early November, an above-average number of weekly pediatric hospitalizations has been reported by the IMPACT network.
  • 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 50, 19 regions (BC (1), AB (4), SK (2), MB (1), ON (6), QC (3) and NS (2)) reported localized activity, and 23 regions (BC (4), AB (1) SK (1), MB (4), ON(1), QC (3), NB (3), NS (1), NL (1), PE (1), YK (1) and NT (2)) reported sporadic activity. Consistent with the early influenza activity this season, a greater number of regions are reporting sporadic and localized activity compared to previous seasons.

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Organization:

Public Health Agency of Canada

Date published: 2017-12-22

Related Topics

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2017-50

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 2017-50
Influenza Surveillance Region Activity Level
Newfoundland - Central No Activity
Newfoundland - Eastern Sporadic
Grenfell Labrador No Activity
Newfoundland - Western No Activity
Prince Edward Island Sporadic
Nova Scotia - Central (Zone 4) Localized
Nova Scotia - Western (Zone 1) Localized
Nova Scotia - Northern (Zone 2) No Activity
Nova Scotia - Eastern (Zone 3) Sporadic
New Brunswick - Public Health Region 1 Sporadic
New Brunswick - Public Health Region 2 No Activity
New Brunswick - Public Health Region 3 No Activity
New Brunswick - Public Health Region 4 No Activity
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 Localized
Québec et Chaudieres-Appalaches Sporadic
Centre-du-Québec Sporadic
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 Sporadic
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 Localized
Saskatchewan - South Localized
Alberta - North Zone Localized
Alberta - Edmonton Localized
Alberta - Central Zone Sporadic
Alberta - Calgary Localized
Alberta - South Zone Localized
British Columbia - Interior Sporadic
British Columbia - Fraser Localized
British Columbia - Vancouver Coastal Sporadic
British Columbia - Vancouver Island Sporadic
British Columbia - Northern Sporadic
Yukon Sporadic
Northwest Territories - North Sporadic
Northwest Territories - South Sporadic
Nunavut - Baffin No Activity
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 50, both influenza A and B detections continued to increase, with 20.9% of tests positive for influenza. The number (1,156) and percentage (15.1%) of influenza A detections for week 50 are above average but within expected levels. The number (448) and percentage of tests (5.8%) positive for influenza B in week 50 are well above expected levels. Current levels of influenza B detections are not typically seen until March. 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 2017-50

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 2017-50
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
50 569 571 16 448

To date this season, 5,829 laboratory-confirmed influenza detections have been reported, of which 79% have been influenza A. Influenza A(H3N2) has been the most common subtype detected this season, representing 95% 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 2017-50

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 2017-50
Reporting
provincesTable Figure 3 - Footnote 1
Week (December 10, 2017 to December 16, 2017) Cumulative (August 27, 2017 to December 16, 2017)
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 50 1 0 49 49 346 38 197 111 141 487
AB 622 9 436 177 220 2669 44 1922 703 719 3388
SK 56 0 38 18 5 239 7 146 86 27 266
MB 43 1 17 25 0 119 5 87 27 2 121
ON 88 2 40 46 30 364 36 207 121 95 459
QC 210 0 0 210 124 613 0 0 613 235 848
NB 26 0 9 17 4 127 0 52 75 8 135
NS 7 0 0 7 0 15 0 0 15 1 16
PE 3 0 3 0 0 14 0 14 0 0 14
NL 1 0 0 1 1 7 0 3 4 2 9
YT 0 0 0 0 7 5 0 5 0 17 22
NT 18 0 18 0 0 31 0 31 0 0 31
NU 1 0 1 0 0 12 0 12 0 1 13
Canada 1125 13 562 550 440 4561 130 2676 1755 1248 5809
PercentageTable Figure 3 - Footnote 2 72% 1% 50% 49% 28% 79% 3% 59% 38% 21% 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 5,379 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 42% have been reported in adults 65 years of age and older. Among cases of influenza A(H3N2), adults aged 65+ represented 52% of cases, compared to 36% and 45% of cases reported at week 50 in the 2016-17 and 2014-15 season 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 2017-50
Age groups (years) Cumulative (August 27, 2017 to December 16, 2017)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 309 29 178 102 75 384 7%
5-19 450 23 231 196 239 689 13%
20-44 802 32 404 366 212 1014 19%
45-64 774 27 428 319 272 1046 19%
65+ 1896 11 1329 556 350 2246 42%
Total 4231 122 2570 1539 1148 5379 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 50, 1.9% of visits to healthcare professionals were due to influenza-like illness. This is an increase compared to the previous week, and slightly below the 5-year average, but remains within the range of previous seasonal levels.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2017-50

Number of Sentinels Reporting in Week 50: 130

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 2017-50
Report week 2017-18 Average Min Max
35 0.5% 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 1.6% 1.5% 1.0% 2.5%
50 1.9% 2.3% 1.3% 3.7%

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 50, 1,342 participants reported to FluWatchers, of which 3% reported symptoms of cough and fever, and 31% of these consulted a healthcare professional. Among participants who reported cough and fever, 92% reported days missed from work or school, resulting in a combined total of 93 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2017-50
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
1342 3% 31% 92% 93

Influenza Outbreak Surveillance

In week 50, there was a sharp increase in the number of reported laboratory-confirmed outbreaks. Fifty-three new laboratory-confirmed influenza outbreaks were reported: 28 in long-term care facilities, 11 in hospitals, and 16 in other settings. Among the 48 with influenza type/subtype reported, seven were associated with influenza B and 39 were associated with influenza A, of which 23 were influenza A(H3N2) and 16 influenza A(unsubtyped). Two were associated with a mix of A(H3N2) and B.

To date this season, 151 influenza/ILI outbreaks have been reported, of which 64 (42%) occurred in LTC facilities. Among the 135 outbreaks for which the influenza type/subtype was reported, 107 were associated with influenza A (of which 75 were A(H3N2)), 22 were associated with influenza B, and three were associated with a mix of A(H3N2) and B. Compared to recent influenza A(H3N2) seasons at week 50, the number of cumulative outbreaks reported this season has been greater than the 2016-17 and 2012-13 seasons, and similar to the 2014-15 season.

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2017-50

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2017-50
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 12 12
50 9 28 16

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 50, 130 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1.

This is a sharp increase from the number of influenza-associated hospitalization reported in week 49. To date this season, 956 influenza-associated hospitalizations have been reported, 87% of which were associated with influenza A, and 645 cases (67%) were in adults 65 years of age or older. The number of cases is considerably elevated relative to this period in the previous two seasons. To date, 70 ICU admissions and 25 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 2017-50

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 2017-50
Age Group Total
0-4 yr 62
5-19 yr 30
20-44 yr 61
45-64 yr 158
65+ yr 645
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 50, 26 laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network. Of the 26 hospitaliations, 16 (62%) were due to influenza A(H3N2). Since week 45, the number of hospitalizations reported each week has been above the seven-season weekly averages.

To date this season, 110 pediatric hospitalizations have been reported by the IMPACT network, 89 of which were associated with influenza A. Twenty-four ICU admissions and fewer than five deaths have been reported. Compared to recent influenza A(H3N2) seasons at week 50, the number of hospitalizations reported this season have been greater than the 2016-17 season, but below the 2014-15 and 2012-13 seasons.

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 2017-50

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 2017-50
Age Group Total
0-5 mo 14
6-23 mo 27
2-4 yr 35
5-9 yr 18
10-16 yr 16

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2017-50

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 2017-50
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 9 5 1 13
47 11 4 0 9
48 19 9 2 23
49 24 15 3 28
50 26 23 4 47
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 214 influenza viruses [160 A(H3N2), 11 A(H1N1)pdm09 and 43 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 2017-50
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 32 Viruses antigenically similar to A/Hong Kong/4801/2014, the A(H3N2) component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent vaccine.
Influenza A (H1N1)
A/Michigan/45/2015-like 11 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
Reduced titer to B/Brisbane/60/2008
(Victoria lineage)
4

Viruses showed reduced titer 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.

B/Phuket/3073/2013-like
(Yamagata lineage)
39 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, 128 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 101 A(H3N2) viruses belonged to genetic group 3C.2a and 27 viruses belonged to subclade 3C.2a1.

Additionally, of the 32 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 29 belonged to genetic group 3C.2a and three viruses belonged to subclade 3C.2a1.

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

Of the four viruses characterized as having reduced titer to ferret antisera produced against cell-propagated B/Brisbane/60/2008, sequence analysis showed that the 4 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 220 influenza viruses for resistance to oseltamivir and zanamivir, and all viruses were sensitive (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2017-50
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 165 0 (0%) 165 0 (0%)
A (H1N1) 11 0 (0%) 11 0 (0%)
B 44 0 (0%) 44 0 (0%)
TOTAL 220 0 (0%) 220 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.

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