FluWatch report: December 17, 2017 to December 30, 2017 (weeks 51 & 52)

Overall Summary
  • Overall, influenza activity continues to increase across Canada. All indicators of influenza activity increased in weeks 51 and 52, but are within the range of expected levels for this time of year.
  • The majority of influenza detections continue to be A(H3N2), although the proportion of detections that are influenza B has been increasing steadily.
  • Influenza B is circulating much earlier than usual this season.The number of influenza B detections remains substantially greater this season compared to previous years.
  • To date this season, the majority of lab confirmations, hospitalizations and deaths 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 weeks 51 and 52, an increasing number of regions reported localized or widespread influenza activity. Among the 45 regions for which data was available in week 52, three regions (BC(1), QC(2)) reported widespread activity, and 22 regions (BC(2), SK(2), MB (4), ON(7), QC(2), NB(2), NS(2) and PE(1)) reported localized activity. Sporadic activity was reported across most of the country.

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Public Health Agency of Canada

Date published: 2018-01-05

Related Topics

Figure 1 - Map of overall influenza/ILI activity level by province and territory, Canada, week 2017-52

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 2017-52
Influenza Surveillance Region Activity Level
Newfoundland - Central  No Activity
Newfoundland - Eastern  Sporadic
Grenfell Labrador No Activity
Newfoundland - Western  No Activity
Prince Edward Island Localized
Nova Scotia - Central (Zone 4) No Activity
Nova Scotia - Western (Zone 1) Localized
Nova Scotia - Northern (Zone 2) No Activity
Nova Scotia - Eastern (Zone 3) Localized
New Brunswick - Public Health Region 1 Sporadic
New Brunswick - Public Health Region 2 Sporadic
New Brunswick - Public Health Region 3 Localized
New Brunswick - Public Health Region 4 Sporadic
New Brunswick - Public Health Region 5 No Activity
New Brunswick - Public Health Region 6 Localized
New Brunswick - Public Health Region 7 Sporadic
Nord-est Québec Sporadic
Québec et Chaudieres-Appalaches Widespread
Centre-du-Québec Widespread
Montréal et Laval Localized
Ouest-du-Québec Sporadic
Montérégie  Localized
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  Localized
Manitoba - Northern Regional Sporadic
Manitoba - Prairie Mountain Localized
Manitoba - South Localized
Manitoba - Winnipeg Localized
Saskatchewan - North  Sporadic
Saskatchewan - Central Localized
Saskatchewan - South Localized
Alberta - North Zone No Data
Alberta - Edmonton No Data
Alberta - Central Zone  No Data
Alberta - Calgary No Data
Alberta - South Zone  No Data
British Columbia - Interior Widespread
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 No Data
Nunavut - Kivalliq No Data
Nunavut - Kitimeot No Data

Laboratory-Confirmed Influenza Detections

In weeks 51 and 52, both influenza A and B detections continued to increase. The proportion of tests positive for influenza increased to 25% in week 51 and 28% in week 52. The proportion of influenza detections that are influenza B has been increasing steadily since week 42. In week 52, 66% of detections were influenza A and 34% influenza B.

The number (1,968) and percentage (18.7%) of influenza A detections for week 52 are close to the seasonal average for this time of year. The number (994) and percentage of tests (9.4%) positive for influenza B in week 52 are well above expected levels. Influenza B is circulating much earlier than usual this season. Current levels of tests positive for influenza B are not typically seen until March. More than 15 times the number of influenza B detections have been reported this season compared to the same period during the past seven seasons. 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 2017-52

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 2017-52
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
51 812 864 50 719
52 1164 776 28 994

To date this season, 11,275 laboratory-confirmed influenza detections have been reported, of which 74% 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 2017-52

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 2017-52
Reporting
provincesTable Figure 3 - Footnote 1
Week (December 17, 2017 to December 30, 2017) Cumulative (August 27, 2017 to December 30, 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 229 41 121 67 281 545 79 318 148 428 973
AB 1,185 16 911 258 481 3916 60 2884 972 1219 5135
SK 76 2 47 27 21 603 16 400 187 107 710
MB 216 1 97 118 16 335 6 185 144 18 353
ON 403 12 200 191 269 766 48 415 303 364 1130
QC 1,116 0 0 1,116 539 1729 0 0 1729 774 2503
NB 103 0 9 94 14 230 0 61 169 22 252
NS 24 0 0 24 1 39 0 0 39 2 41
PE 15 0 15 0 11 29 0 29 0 11 40
NL 2 0 0 2 3 9 0 3 6 5 14
YT 0 0 0 0 12 5 0 5 0 29 34
NT 40 0 40 0 3 73 0 73 0 3 76
NU 1 0 1 0 0 13 0 13 0 1 14
Canada 3410 72 1441 1897 1651 8292 209 4386 3697 2983 11275
PercentageTable Figure 3 - Footnote 2 67% 2% 42% 56% 33% 74% 3% 53% 45% 26% 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 10,336 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, 44% have been reported in adults 65 years of age and older. Among cases of influenza A(H3N2), adults 65 years of age and older represented 51% of cases, compared to 39% and 54% of cases reported in the same period in the 2016-17 and 2014-15 season, respectively. Cases of influenza B this season were distributed more evenly across all age-groups, with 36% of cases in adults 65 years of age and older, 23% of cases in adults 45-64 years of age, and 23% in children and adults under 20 years of age.

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 2017-52
Age groups (years) Cumulative (August 27, 2017 to December 30, 2017)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 629 40 325 264 140 769 7%
5-19 764 38 387 339 462 1226 12%
20-44 1363 55 676 632 468 1831 18%
45-64 1351 47 682 622 610 1961 19%
65+ 3588 17 2165 1406 961 4549 44%
Total 7695 197 4235 3263 2641 10336 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 52, 4.5% of visits to healthcare professionals were due to influenza-like illness (ILI); an increase compared to the previous week. Since week 49, the weekly proportion of healthcare visits for ILI has been similar to the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2017-35 to 2017-52

Number of Sentinels Reporting in Week 52: 72

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 2017-52
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 4.5% 4.5% 1.7% 7.1%

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 52, 1,202 participants reported to FluWatchers, of which 6% reported symptoms of cough and fever, and 10% of these consulted a healthcare professional. Among participants who reported cough and fever, 78% reported days missed from work or school, resulting in a combined total of 180 missed days of work or school.

Table 2 - Summary of influenza-like illness symptoms reported by participating Canadians, Canada, week 2017-52
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
1202 6% 10% 78% 180

Influenza Outbreak Surveillance

In weeks 51 and 52, the number of reported laboratory-confirmed outbreaks of influenza increased. During this period, 137 new influenza outbreaks were reported: 97 in long-term care facilities, 12 in hospitals, and 28 in other settings. Among the 102 outbreaks with influenza type/subtype reported, 27 were associated with influenza B, and 69 were associated with influenza A, of which 21 were influenza A(H3N2) and 48 influenza A(unsubtyped). Six outbreaks were associated with a mix of influenza A and B.

To date this season, 293 influenza/ILI outbreaks have been reported, of which 166 (57%) occurred in LTC facilities. Among the 239 outbreaks for which the influenza type/subtype was reported, 179 were associated with influenza A (of which 99 were A(H3N2)), 51 were associated with influenza B, and nine were associated with a mix of A and B. Compared to recent influenza A(H3N2) seasons at week 52 or 53, the number of cumulative outbreaks reported this season has been slightly 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 2017-52

Figure 5
Figure 5 - Text Description
Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2017-35 to 2017-52
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 13 12
50 9 32 16
51 8 42 15
52 4 55 13

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In weeks 51 and 52, 94 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1. However, this is an underrepresentation of the number of hospitalizations for this period, due to gaps in reporting. Retrospective updates will be included in the next FluWatch report.

To date this season, 1,050 influenza-associated hospitalizations have been reported, 87% of which were associated with influenza A, and 710 cases (68%) were in adults 65 years of age or older. To date, 93 ICU admissions and 34 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 2017-52

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 2017-52
Age Group Total
0-4 yr 70
5-19 yr 40
20-44 yr 62
45-64 yr 168
65+ yr 710
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 weeks 51 and 52, the number of laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalizations reported by the Immunization Monitoring Program Active (IMPACT) network continued to increase. A total of 84 hospitaliations were reported in this two-week period, of which 54 (64%) were due to influenza A. After several weeks above average, the number of hospitalizations reported in week 52 was similar to the seven-season weekly average.

To date this season, 195 pediatric hospitalizations have been reported by the IMPACT network, 144 (74%) of which were associated with influenza A. Thirty-five ICU admissions and fewer than five deaths have been reported. Compared to recent influenza A(H3N2) seasons at week 52, 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 2017-52

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 2017-52
Age Group Total
0-5 mo 18
6-23 mo 49
2-4 yr 51
5-9 yr 39
10-16 yr 38

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, weeks 2017-35 to 2017-52

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 2017-52
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 12 4 0 9
48 18 9 2 23
49 24 15 3 28
50 26 23 4 47
51 39 32 4 72
52 45 47 7 92
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 273 influenza viruses [190 A(H3N2), 20 A(H1N1)pdm09 and 63 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 2017-52
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 52 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 20 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)
1 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)
5 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)
57 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, 138 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 111 A(H3N2) viruses belonged to genetic group 3C.2a and 27 viruses belonged to subclade 3C.2a1.

Additionally, of the 52 influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, 29 belonged to genetic group 3C.2a and four viruses belonged to subclade 3C.2a1. Sequencing is pending for the remaining 19 viruses.

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 five viruses had a two amino acids deletion in the HA gene.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 287 influenza viruses for resistance to oseltamivir, and 226 for resistance to zanamivir. All viruses were sensitive to these neuraminidase inhibitors (Table 4).

Table 4 - Antiviral resistance by influenza virus type and subtype, Canada, weeks 2017-35 to 2017-52
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 206 0 (0%) 168 0 (0%)
A (H1N1) 20 0 (0%) 12 0 (0%)
B 61 0 (0%) 46 0 (0%)
TOTAL 287 0 (0%) 226 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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