FluWatch report: October 28 to November 4, 2017 (week 44)

Overall Summary
  • Influenza activity continues to increase, but remained below the seasonal threshold in week 44.
  • The percentage of laboratory tests positive for both influenza A and B is higher for this time of year compared to previous seasons. The majority of influenza detections continue to be A(H3N2).
  • The number of influenza-related hospitalizations and regions reporting sporadic activity are above the expected levels for this time of year.
  • 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 44, one region in British Columbia reported localized activity, and 23 regions (British Columbia (2), Alberta (5), Saskatchewan (2), Ontario (5), Quebec (5), New Brunswick (2), Prince Edward Island (1) and Newfoundland and Labrador (1)) reported sporadic activity. Consistent with the increased number of influenza detections this season, a greater number of regions are reporting sporadic activity compared to previous seasons.

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Public Health Agency of Canada

Date published: 2017-11-10

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Figure 1 – Map of overall influenza/ILI activity level by province and territory, Canada, 2017-18, Week 44

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
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) No Activity
Nova Scotia - Western (Zone 1) No Activity
Nova Scotia - Northern (Zone 2) No Activity
Nova Scotia - Eastern (Zone 3) No Activity
New Brunswick - Public Health Region 1 Sporadic
New Brunswick - Public Health Region 2 No Activity
New Brunswick - Public Health Region 3 Sporadic
New Brunswick - Public Health Region 4 No Activity
New Brunswick - Public Health Region 5 No Activity
New Brunswick - Public Health Region 6 No Activity
New Brunswick - Public Health Region 7 No Activity
Nord-est Québec No Activity
Québec et Chaudieres-Appalaches Sporadic
Centre-du-Québec Sporadic
Montréal et Laval Sporadic
Ouest-du-Québec Sporadic
Montérégie  Sporadic
Ontario - Central East Sporadic
Ontario - Central West Sporadic
Ontario - Eastern Sporadic
Ontario - North East Sporadic
Ontario - North West  No Activity
Ontario - South West  No Activity
Ontario - Toronto Sporadic
Manitoba - Interlake-Eastern  No Activity
Manitoba - Northern Regional No Activity
Manitoba - Prairie Mountain No Activity
Manitoba - South No Activity
Manitoba - Winnipeg No Activity
Saskatchewan - North  Sporadic
Saskatchewan - Central Sporadic
Saskatchewan - South No Activity
Alberta - North Zone Sporadic
Alberta - Edmonton Sporadic
Alberta - Central Zone  Sporadic
Alberta - Calgary Sporadic
Alberta - South Zone  Sporadic
British Columbia - Interior Sporadic
British Columbia - Fraser  Localized
British Columbia - Vancouver Coastal No Activity
British Columbia - Vancouver Island Sporadic
British Columbia - Northern No Activity
Yukon No Activity
Northwest Territories - North No Data
Northwest Territories - South No Data
Nunavut - Baffin No Activity
Nunavut - Kivalliq No Activity
Nunavut - Kitimeot No Activity

Laboratory Confirmed Influenza Detections

In week 44, the number of both influenza A and B detections increased, although the percentage of tests positive for influenza remained similar to the previous week at 4.5%, which is below the seasonal threshold. The number and percentage of both influenza A and B tests positive is higher for this time of year than was observed during the previous 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, 2017-18, weeks 35 to 44

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 start and end 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, 2017-18
Report Week A(Unsubtyped) A(H3) A(H1)pdm09 Influenza B
35 4 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 44 106 3 21
44 51 107 3 29

To date this season, 900 laboratory-confirmed influenza detections have been reported, of which 88% 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, 2017-18, week 44

Figure 3
Figure 3 - Text Description
Figure 3 - Cumulative numbers of positive influenza specimens by type/subtype and province/territory, Canada, 2017-18
Reporting
provincesTable Figure 3 - Footnote 1
Week (October 29, 2017 to November 4, 2017) Cumulative (August 27, 2017 to November 4, 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 9 1 8 0 4 150 9 124 17 19 169
AB 84 1 64 19 17 354 9 278 67 50 404
SK 2 0 1 1 0 26 0 20 6 1 27
MB 1 0 0 1 0 4 0 3 1 0 4
ON 13 0 11 2 1 101 13 57 31 12 113
QC 15 0 0 15 6 74 0 0 74 17 91
NB 33 0 21 12 0 63 0 30 33 2 65
NS 2 0 0 2 0 4 0 0 4 0 4
PE 1 0 1 0 0 6 0 6 0 0 6
NL 0 0 0 0 1 4 0 3 1 1 5
YT 0 0 0 0 0 5 0 4 1 3 8
NT 0 0 0 0 0 0 0 0 0 0 0
NU 1 0 1 0 0 3 0 3 0 1 4
Canada 161 2 107 52 29 794 31 528 235 106 900
PercentageTable Figure 3 - Footnote 2 85% 1% 66% 32% 15% 88% 4% 66% 30% 12% 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 738 laboratory-confirmed influenza cases (Table 1). Among all influenza cases with reported age and type/subtype information, approximately one half of the cases have been reported in adults 65 years of age and older. This proportion was higher among cases of influenza A (52%) compared to influenza B (32%).

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age-group reported through case-based laboratory reporting, Canada, 2017-18, week 44
Age groups (years) Cumulative (August 27, 2017 to November 4, 2017)
Influenza A B Influenza A and B
A Total A(H1) pdm09 A(H3) A (UnS)Table 1 Footnote 1 Total # %
0-4 36 7 22 7 11 47 6%
5-19 38 4 23 11 14 52 7%
20-44 106 5 71 30 13 119 16%
45-64 131 9 80 42 21 152 21%
65+ 340 3 270 67 28 368 50%
Total 651 28 466 157 87 738 100%
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 44, 1.6% of visits to healthcare professionals were due to influenza-like illness; a slight decrease compared to the previous week, but remains slightly above the 5-year average.

Figure 4 - Percentage of visits for ILI reported by sentinels by report week, Canada, 2017-18, weeks 35 to 44

Number of Sentinels Reporting in Week 44: 129

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, 2017-18
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 1.2% 1.3% 0.9% 1.6%
41 1.8% 1.4% 0.9% 2.4%
42 1.6% 1.4% 1.0% 1.9%
43 1.8% 1.3% 1.0% 1.5%
44 1.6% 1.3% 0.9% 1.6%

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 44, 1351 participants reported to FluWatchers, of which 1% reported symptoms of cough and fever in the preceding week and 20% of these consulted a healthcare professional. Among participants who reported cough and fever, 75% reported days missed from work or school, resulting in a combined total of 34 missed days.

Table 2 – Summary of influenza-like illness symptoms reported by participating Canadians, Canada, 2017-18, week 44
Number of Participants Reporting Percentage participants reporting Cough and Fever Percentage of participants with cough and fever who consulted a healthcare professional Facilities Percentage of participants with cough and fever who reported missed days from work or school Number of missed days from work or school
1351 1% 20% 75% 34

Influenza Outbreak Surveillance

In week 44, one new laboratory-confirmed influenza outbreak was reported in a long-term care facility.

To date this season, 18 influenza/ILI outbreaks have been reported, of which 8 occurred in LTC facilities. Among the 12 outbreaks for which the influenza type/subtype was reported, 9 were associated with influenza A. The number of outbreaks to date is within the expected range for this time of year.

Figure 5 - Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, 2017-18, weeks 35 to 44

Figure 5
Figure 5 - Text Description
Figure 5 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2017-18
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 0
42 0 2 0
43 3 1 0
44 0 1 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

In week 44, 15 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1.

To date this season, 159 influenza-associated hospitalizations have been reported, 93% of which were associated with influenza A, and 115 cases (72%) 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. Eight ICU admissions and eight deaths have been reported.

Figure 6 - Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, 2017-18

Figure 6
Figure 6 - Text Description
Cumulative numbers of hospitalizations by age-group reported by participating provinces and territories, 2017-18
Age Group Total
0-4 yr 7
5-19 yr 8
20-44 yr 9
45-64 yr 20
65+ yr 115
Footnote 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 footnote 1 referrer

Pediatric Influenza Hospitalizations and Deaths

In week 44, one laboratory-confirmed influenza-associated pediatric (≤16 years of age) hospitalization was reported by the Immunization Monitoring Program Active (IMPACT) network.

To date this season, 17 pediatric hospitalizations have been reported by the IMPACT network, 14 of which were associated with influenza A. Six ICU admissions and no deaths have been reported. The number of hospitalizations reported this season has been similar compared to the same period in recent seasons in which influenza A(H3N2) was the predominant circulating subtype (2014-15, 2016-17).

Figure 7 - Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2017-18 weeks 35-44

Figure 7
Figure 7 - Text Description
Cumulative numbers of pediatric hospitalizations (≤16 years of age) with influenza by type and age-group reported by the IMPACT network, Canada, 2017-18
Age Group Total
0-5 mo <5
6-23 mo <5
2-4 yr <5
5-9 yr <5
10-16 yr 5

Figure 8 - Number of pediatric hospitalizations (≤16 years of age) with influenza reported by the IMPACT network, by week, Canada, 2017-18 weeks 35-44

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, 2017-18 weeks 35-43
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

Influenza Strain Characterizations

During the 2017-18 influenza season, the National Microbiology Laboratory (NML) has characterized 52 influenza viruses [41 A(H3N2), 5 A(H1N1)pdm09 and 6 B viruses] that were received from Canadian laboratories.

Antigenic Characterization

Among influenza viruses characterized by hemagglutination inhibition assay during the 2017-18 season, all viruses were antigenically similar to the cell-culture propagated reference strains recommended by WHO.

Table 3 - Influenza antigenic strain characterizations, Canada, 2017-18 weeks 35- 44
Strain Characterization Results Count Description
Influenza A (H3N2)
A/Hong Kong/4801/2014-like 7 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 5 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, the influenza B component of the 2017-18 Northern Hemisphere's trivalent and quadrivalent influenza vaccine. . 
B/Phuket/3073/2013-like
(Yamagata lineage)
5 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, 34 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 24 H3N2 viruses belonged to genetic group 3C.2a and 10 viruses belonged to subclade 3C.2a1.

Additionally, of the seven influenza A(H3N2) viruses that were characterized antigenically as similar to A/Hong Kong/4801/2014, six belonged to genetic group 3C.2a and one virus 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.

Antiviral Resistance

During the 2017-18 season, the National Microbiology Laboratory (NML) has tested 50 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, 2017-18 weeks 35-44
Virus type and subtype Oseltamivir Zanamivir
# tested # resistant (%) # tested # resistant (%)
A (H3N2) 39 0 (0%) 39 0 (0%)
A (H1N1) 5 0 (0%) 5 0 (0%)
B 6 0 (0%) 6 0 (0%)
TOTAL 50 0 (0%) 50 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

Influenza/Influenza-like Illness (ILI) Activity
Influenza/ILI activity levels, as represented on the map, are assigned and reported by Provincial and Territorial Ministries of Health, based on laboratory confirmations, primary care consultations for ILI and reported outbreaks. ILI data may be reported through sentinel physicians, emergency room visits or health line telephone calls, and the detemination of an increase is based on the assessment of the provincial/territorial epidemiologist. Maps from previous weeks, including any retrospective updates, are available in the mapping feature found in the Weekly Influenza Reports.

Influenza/ILI activity level

1 = No activity: no laboratory-confirmed influenza detections in the reporting week, however, sporadically occurring ILI may be reported

2 = Sporadic: sporadically occurring ILI and lab confirmed influenza detection(s) with no outbreaks detected within the influenza surveillance region Footnote

3 = Localized:

  1. evidence of increased ILIFootnote * and
  2. lab confirmed influenza detection(s) together with
  3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in less than 50% of the influenza surveillance regionFootnote

4 = Widespread:

  1. evidence of increased ILIFootnote * and
  2. lab confirmed influenza detection(s) together with
  3. outbreaks in schools, hospitals, residential institutions and/or other types of facilities occurring in greater than or equal to 50% of the influenza surveillance regionFootnote
Footnote *

More than just sporadic as determined by the provincial/territorial epidemiologist.

Return to footnote * referrer

Footnote †

Influenza surveillance regions within the province or territory as defined by the provincial/territorial epidemiologist.

Return to footnote referrer

Laboratory-Confirmed Influenza Detections
Provincial, regional and some hospital laboratories report the weekly number of tests and detections of influenza and other respiratory viruses. Provincial public health laboratories submit demographic information for cases of influenza. This case-level data represents a subset of influenza detections reported through aggregate reporting. Specimens from NT, YT, and NU are sent to reference laboratories in the provinces for testing. Cumulative data includes updates to previous weeks. Discrepancies in values in Figures 2 and 3 may be attributable to differing data sources.

Syndromic/Influenza-like Illness Surveillance
FluWatch maintains a network of primary care practitioners who report the weekly proportion of ILI cases seen in their practice. Independent sentinel networks in BC, AB, and SK compile their data for reporting to FluWatch. Not all sentinel physicians report every week.

Definition of Influenza-like-illness (ILI): Acute onset of respiratory illness with fever and cough and with one or more of the following - sore throat, arthralgia, myalgia, or prostration which is likely due to influenza. In children under 5 years of age, gastrointestinal symptoms may also be present. In patients under 5 or 65 years and older, fever may not be prominent.

Influenza Outbreak Surveillance
Outbreaks of influenza or ILI are reported from all provinces and territories, according to the definitions below. However, reporting of outbreaks of influenza/ILI from different types of facilities differs between jurisdictions. All provinces and territories with the exception of NU report influenza outbreaks in long-term care facilities. All provinces and territories with the exception of NU and QC report outbreaks in hospitals.

Outbreak definitions:
Schools: Greater than 10% absenteeism (or absenteeism that is higher (e.g. >5-10%) than expected level as determined by school or public health authority) which is likely due to ILI.
Hospitals and residential institutions: two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case of influenza. Residential institutions include but are not limited to long-term care facilities (LTCF) and prisons.
Workplace: Greater than 10% absenteeism on any day which is most likely due to ILI.
Other settings: two or more cases of ILI within a seven-day period, including at least one laboratory-confirmed case of influenza; i.e. closed communities.

Serious Outcome Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
Influenza-associated hospitalizations and deaths are reported by 8 Provincial and Territorial Ministries of Health (excluding BC, NU, ON and QC). The hospitalization or death does not have to be attributable to influenza, a positive laboratory test is sufficient for reporting. Only hospitalizations that require intensive medical care are reported by SK.
Due to changes in participating provinces and territories, comparisons to previous years should be done with caution.
Pediatric Influenza Hospitalizations and Deaths
The Immunization Monitoring Program Active (IMPACT) network reports the weekly number of hospitalizations with influenza among children admitted to one of the 12 participating paediatric hospitals in 8 provinces. These represent a subset of all influenza-associated pediatric hospitalizations in Canada.

Influenza Strain Characterizations and Antiviral Resistance
Provincial public health laboratories send a subset of influenza virus isolates to the National Microbiology Laboratory for strain characterization and antiviral resistance. These represent a subset of all influenza detections in Canada and the proportion of isolates of each type and subtype is not necessarily representative of circulating viruses.
Antigenic strain characterization data reflect the results of hemagglutination inhibition (HI) testing compared to the reference influenza strains recommended by WHO. Genetic strain characterization data are based on analysis of the sequence of the viral hemagglutinin (HA) gene.

Antiviral resistance testing is conducted by phenotypic and genotypic methods on influenza virus isolates submitted to the National Microbiology Laboratory. All isolates are tested for oseltamivir and zanamivir and a subset are tested for resistance to amantadine.

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).

This report is available on the Government of Canada Influenza webpage.
Ce rapport est disponible dans les deux langues officielles.

We would like to thank all the Fluwatch surveillance partners who are participating in this year's influenza surveillance program.

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