FluWatch report: November 24 to 30, 2019 (week 48) 

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Organization: Public Health Agency of Canada

Date published: 2019-12-06

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Overall Summary

  • The flu season started in week 47 at the national level, and activity continues to increase as expected for this time of year.
  • Influenza A(H3N2) continues to be the most common influenza virus circulating in Canada for the season to date; however, approximately 40% of influenza A detections were A(H1N1) in week 48.
  • Although the majority of laboratory detections have been influenza A to date this season, the proportion of detections of influenza B (30%) is higher than average for this time of year.

Influenza/Influenza-like Illness Activity (geographic spread)

During week 48, the number of regions reporting influenza activity increased compared to the previous week (Figure 1).

Figure 1 – Map of influenza/ILI activity by province and territory, Canada, week 2019-48

Number of Regions Reporting in Week 48: 53 out of 53

Figure 1. Text equivalent follows.

Figure 1 - Text equivalent
Province Influenza Surveillance Region Activity Level
N.L. Eastern No Activity
N.L. Labrador-Grenfell No Activity
N.L. Central Sporadic
N.L. Western No Activity
P.E.I. Prince Edward Island Sporadic
N.S. Zone 1 - Western No Activity
N.S. Zone 2 - Northern No Activity
N.S. Zone 3 - Eastern No Activity
N.S. Zone 4 - Central No Activity
N.B. Region 1 Sporadic
N.B. Region 2 No Activity
N.B. Region 3 Sporadic
N.B. Region 4 No Activity
N.B. Region 5 No Activity
N.B. Region 6 No Activity
N.B. Region 7 No Activity
Que. Nord-est Sporadic
Que. Québec et Chaudieres-Appalaches Sporadic
Que. Centre-du-Québec Sporadic
Que. Montréal et Laval Sporadic
Que. Ouest-du-Québec Sporadic
Que. Montérégie Sporadic
Ont. Central East Sporadic
Ont. Central West Sporadic
Ont. Eastern Localized
Ont. North East Sporadic
Ont. North West Sporadic
Ont. South West Sporadic
Ont. Toronto Localized
Man. Northern Regional Sporadic
Man. Prairie Mountain Sporadic
Man. Interlake-Eastern Sporadic
Man. Winnipeg Localized
Man. Southern Health No Activity
Sask. North No Activity
Sask. Central Sporadic
Sask. South Sporadic
Alta. North Zone Sporadic
Alta. Edmonton Sporadic
Alta. Central Zone Localized
Alta. Calgary Localized
Alta. South Zone Localized
B.C. Interior Sporadic
B.C. Fraser Sporadic
B.C. Vancouver Coastal Sporadic
B.C. Vancouver Island Sporadic
B.C. Northern Sporadic
Y.T. Yukon No Activity
N.W.T. North No Activity
N.W.T. South No Activity
Nvt. Qikiqtaaluk No Activity
Nvt. Kivalliq No Activity
Nvt. Kitimeot No Activity

Laboratory-Confirmed Influenza Detections

In week 48, the number of detections of influenza continued to increase. The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):

To date this season (weeks 35 to 48), 1,785 laboratory detections of influenza were reported:

Detailed information on age and type/subtype has been received for 1,457 laboratory-confirmed influenza cases (Table 1).

To date this season (weeks 35 to 48):

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 2 - Number of positive influenza tests and percentage of tests positive, by type, subtype and report week, Canada, weeks 2019-35 to 2019-48

Number of Laboratories Reporting in Week 48: 34 out of 34

Figure 2. Text equivalent follows.

Figure 2 - Text equivalent
Surveillance Week A(Unsubtyped) A(H3N2) A(H1N1)pdm09 Influenza B Percent Positive A Percent Positive B
35 10 16 0 2 1.3 0.1
36 11 13 2 2 1.1 0.1
37 5 17 2 5 0.9 0.2
38 11 15 3 6 1.0 0.2
39 11 21 2 3 1.0 0.1
40 34 9 1 2 1.2 0.1
41 34 18 0 5 1.4 0.1
42 54 12 1 14 1.6 0.3
43 44 13 7 17 1.6 0.3
44 43 23 16 17 1.8 0.3
45 57 57 20 39 2.2 0.7
46 82 43 23 77 2.7 1.4
47 103 50 33 122 3.1 2.0
48 204 58 40 208 4.8 3.2

Figure 3 – Distribution of positive influenza specimens by type/subtype and province/territoryFootnote *, Canada, weeks 2019-35 to 2019-48

Figure 3. Text equivalent follows.

Footnote *

Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces. However, data on laboratory-confirmed detections of influenza from Nunavut are not currently available

Return to footnote * referrer

Figure 3 - Text equivalent
Provinces Table Figure 3 - Footnote 1 Cumulative (August 25, 2019 to November 23, 2019)
A Total A(H1N1) A(H3N2) A(UnS)Table Figure 3 - Footnote 3 B Total A & B Total
B.C. 212 21 79 64 24 236
Alta. 363 76 185 102 261 624
Sask. 77 0 0 43 17 94
Man. 43 7 17 19 58 101
Ont. 143 39 59 45 46 189
Que. 376 0 0 376 105 481
N.B. 14 3 2 9 4 18
N.S. 2 0 0 2 1 3
P.E.I. 3 0 0 3 2 5
N.L. 17 0 15 2 1 18
Y.T. 11 0 8 3 0 11
N.W.T 5 4 0 1 0 5
Nvt. 0 0 0 0 0 0
Canada 1266 150 365 669 519 1785
PercentageTable Figure 3 - Footnote 2 71% 12% 29% 53% 29% 100%
Table Figure 3 - Footnote 1

Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces. However, data on laboratory-confirmed detections of influenza from Nunavut are not currently available.

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 Table Figure 3 - Footnote 3 referrer

Table 1 - Cumulative numbers of positive influenza specimens by type, subtype and age group reported through case-based laboratory reporting, Canada, weeks 2019-35 to 2019-48
Age groups
(years)
Cumulative (August 25, 2019 to November 30, 2019)
Influenza A B Influenza A and B
A Total A(H1N1) A(H3N2) A (Un subtyped)1 Total # %
0-4 130 25 38 67 69 199 14%
5-19 122 9 40 73 183 305 21%
20-44 183 30 51 102 144 327 22%
45-64 204 43 56 105 23 227 16%
65+ 379 19 139 221 20 399 27%
Total 1018 126 324 568 439 1457 100%
Table 1 Footnote 1

Unsubtyped: The specimen was typed as influenza A, but no result for subtyping was available.

Table 1 Return to footnote 1 referrer

Syndromic / Influenza-like Illness Surveillance

Healthcare Professionals Sentinel Syndromic Surveillance

In week 48, 1.3% of visits to healthcare professionals were due to influenza-like illness (ILI) which is slightly below the average for this time of year (1.5%) (Figure 4).

Figure 4 – Percentage of visits for ILI reported by sentinels by report week, Canada, weeks 2019-35 to 2019-48

Number of participants reporting in week 48: 72

Figure 4

The shaded area represents the maximum and minimum percentage of visits for ILI reported by week from seasons 2014-2015 to 2018-2019

Figure 4 - Text equivalent
Surveillance Week 2019-20 Average Min Max
35 0.6% 0.6% 0.4% 0.9%
36 0.4% 0.6% 0.4% 0.9%
37 0.7% 0.7% 0.5% 1.0%
38 1.1% 0.7% 0.6% 1.0%
39 0.8% 0.9% 0.5% 1.2%
40 1.0% 1.2% 0.8% 1.7%
41 0.9% 1.7% 0.8% 2.8%
42 1.1% 1.6% 1.2% 2.1%
43 0.7% 1.2% 0.8% 1.7%
44 0.9% 1.2% 0.7% 1.7%
45 0.8% 1.2% 0.9% 1.5%
46 1.3% 1.4% 1.2% 1.8%
47 1.5% 1.6% 1.1% 2.2%
48 1.3% 1.5% 1.1% 2.2%

FluWatchers

In week 48, 3,104 participants reported to FluWatchers, of which 1.6% (51) reported symptoms of cough and fever (Figure 5).

Among the 51 participants who reported cough and fever:

If you are interested in becoming a FluWatcher, sign up today.

Figure 5 - Percentage of participants reporting fever and cough, Canada, weeks 2019-40 to 2019-48

Number of Participants Reporting in Week 48: 3,104

Figure 5. Text equivalent follows.

Figure 5 - Text equivalent
Surveillance Week % cough and fever
40 2.2%
41 1.8%
42 1.7%
43 2.2%
44 1.6%
45 1.4%
46 1.2%
47 1.5%
48 1.6%

Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2019-48

Click on the map to access the link

map

Influenza Outbreak Surveillance

In week 48, eight new outbreaks were reported: four in long term care facilities, one in an acute care facility, one in a school/daycare and two in facilities categorized as ‘other’, which includes facilities such as private personal care homes, correctional facilities, and colleges/universities (Figure 6).

To date this season, a total of 33 laboratory-confirmed influenza outbreaks have been reported; eighteen in long-term care facilities, two in a schools/daycares, three in acute care facilities and ten in a facilities categorized as ‘other’. Of the outbreaks where influenza type was reported (31), twenty-five were due to influenza A. Among the 14 outbreaks for which the influenza A subtype was reported, all were associated with A(H3N2). One ILI outbreak in a school/daycare has also been reported.

Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2019-35 to 2019-48

Number of provinces and territories reporting in week 48: 13 out of 13

Figure 6

Figure 6 - Text equivalent
Surveillance Week Acute Care Facilities Long Term Care Facilities Other Schools and Daycares Remote and/or Isolated Communities
35 0 0 0 0 0
36 0 0 0 0 0
37 0 0 0 0 0
38 0 1 0 0 0
39 0 1 0 0 0
40 0 2 0 0 0
41 0 2 1 0 0
42 1 0 0 0 0
43 0 0 1 0 0
44 0 0 1 0 0
45 0 2 4 0 0
46 1 4 0 0 0
47 0 2 1 1 0
48 1 4 2 1 0

Severe Outcomes Influenza Surveillance

Provincial/Territorial Influenza Hospitalizations and Deaths

To date this season. 152 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1.

Nineteen ICU admissions and no deaths have been reported.

Number of provinces and territories reporting in week 48: 9 out of 9
Footnote 1

Influenza-associated hospitalizations are reported by N.L., P.E.I. N.S., N.B., Man., Alb., Y.T. and N.W.T. Only hospitalizations that require intensive medical care are reported by Sask. The cumulative rate of hospitalizations is calculated using the population by age-group in participating provinces and territories.

Footnote 1 referrer

Pediatric Influenza Hospitalizations and Deaths

In week 48, 21 pediatric (≤16 years of age) laboratory-confirmed influenza-associated hospitalizations were reported by the Immunization Monitoring Program Active (IMPACT) network (Figure 7). This is slightly above the average (18) for week 48 over the previous five seasons.

To date this season, 43 pediatric hospitalizations have been reported by the IMPACT network; 58% (25) of cases were associated with influenza A and 42 % (18) with influenza B. Among the 10 cases for which the influenza A subtype was reported, 70% (7) were associated with A(H1N1).

Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2019-35 to 2019-48

Figure 7

The shaded area represents the maximum and minimum number of cases reported by week from seasons 2014-15 to 2018-19

Figure 7 - Text equivalent
Surveillance week 2019-2020 Average Min Max
35 0 0 0 1
36 2 0 0 1
37 0 1 0 2
38 0 1 0 2
39 1 1 0 3
40 0 1 0 2
41 2 1 0 3
42 2 2 0 5
43 3 5 2 12
44 1 5 1 15
45 1 10 2 37
46 6 13 1 41
47 5 13 2 36
48 21 18 2 40

Distribution of antigenic phenotype among characterized influenza viruses, Canada, weeks 2019-35 to 2019-48

Adult Influenza Hospitalizations and Deaths

Surveillance of laboratory-confirmed influenza-associated adult (≥16 years of age) hospitalizations by the Canadian Immunization Research Network (CIRN) Serious Outcomes Surveillance (SOS) network began on November 1st for the 2019-20 season. To date this season, 14 cases have been reported.

Influenza Strain Characterizations

From September 1 to December 5, 2019, the National Microbiology Laboratory (NML) has characterized 80 influenza viruses (44 A(H3N2), 21 A(H1N1) and 15 influenza B) that were received from Canadian laboratories.

Influenza A(H3N2)

Over recent years, circulating strains of A(H3N2) have evolved, and are increasingly difficult to characterize by hemagglutination inhibition (HI) assay. Genetic characterization is established by sequencing the hemagglutinin (HA) gene of the influenza viruses to compare their genetic properties.

Antigenic Characterization:

Among the 14 influenza A(H3N2) viruses antigenically characterized to date, the majority (79%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017 (Figure 8a).

Genetic Characterization:

Nearly all (93%) of the 40 A(H3N2) viruses genetically characterized this season belonged to genetic group 3C.2a1b based on sequence analysis of the HA gene. Three viruses belonged to the genetic group 3C.3a (Figure 9).

Group 3C.2a1b viruses analysed represent:

A/Kansas/14/2017 belongs to genetic group 3C.3a and is the influenza A(H3N2) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza A(H1N1)

Among the 21 A(H1N1) viruses characterized to date, all were antigenically similar to A/Brisbane/02/2018 by HI testing using antiserum raised against egg-propagated A/Brisbane/02/2018 (Figure 8b). A/Brisbane/02/2018 is the influenza A(H1N1) component of the 2019-20 Northern Hemisphere influenza vaccine.

Influenza B

Among the 15 influenza B viruses antigenically characterized this season, all belonged to the B/Victoria lineage, and the majority (60%) showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 8c).

Sequence analysis showed that all of the nine viruses showing reduced titre had a three amino acid deletion (162-164) in the HA gene.

The recommended influenza B components for the 2019-20 Northern Hemisphere influenza vaccine are B/Colorado/06/2017 (Victoria lineage) and B/Phuket/3073/2013 (Yamagata lineage). B/Phuket/3073/2013 is included in the quadrivalent influenza vaccine.

Figure 8 - Distribution of antigenic phenotypes among characterized influenza viruses, Canada, September 1 to December 5, 2019

Figure 8

Figure 8 - Text equivalent
A) A(H3N2) viruses - Number of viruses characterized: 14
Antigenic phenotype of A(H3N2) virus Number of viruses Percentage
A/Kansas/14/2017-like 3 21%
Reduced titer to A/Kansas/14/2017 11 79%
B) A(H1N1) viruses - Number of viruses characterized: 21
Antigenic phenotype of A(H1N1) virus Number of viruses Percentage
A/Brisbane/02/2018-like 21 100%
Reduced titer to A/Brisbane/02/2018 0 0%
C) B viruses -Number of viruses characterized: 15
Antigenic phenotype of influenza B virus Number of viruses Percentage
B/Colorado/06/2017-like 6 40%
Reduced titer to B/Colorado/06/2017 9 60%
B/Phuket/3073/2013-like 0 0%
Figure 9 – Distribution of genetic clades among characterized A(H3N2) influenza viruses, Canada, September 1 to December 5, 2019

Figure 9

Figure 9 - Text Description
Number of viruses sequenced: 40
Genetic Clade of A(H3N2) virus Number of viruses Percentage
Subclade 3C.2a1b 37 93%
Clade 3C.3a 3 8%

Antiviral Resistance

The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance.

Oseltamivir:

75 influenza viruses (41 A(H3N2), 18 A(H1N1) and 16 B) were tested for resistance to oseltamivir

Zanamivir:

75 influenza viruses (41 A(H3N2), 18 A(H1N1) and 16 B) were tested for resistance to zanamivir:

Amantadine:

High levels of resistance to amantadine persist among influenza A(H1N1) and influenza A(H3N2) viruses. All viruses tested this season were resistant.

Vaccine Monitoring

Vaccine monitoring refers to activities related to the monitoring of influenza vaccine coverage and effectiveness.

Vaccine Coverage

Influenza vaccine coverage estimates for the 2019-20 season are anticipated to be available in February or March 2020.

Vaccine Effectiveness

Influenza vaccine effectiveness estimates for the 2019-20 season are anticipated to be available in February or March 2020.

Provincial and International Surveillance Links

Notes

The data in the FluWatch report represent surveillance data available at the time of writing. All data are preliminary and may change as more reports are received.

To learn more about the FluWatch program, see the Overview of influenza monitoring in Canada page.

For more information on the flu, see our Flu (influenza) web page.

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

This report is available on the Government of Canada Influenza webpage.
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