FluWatch report: December 8 to 14, 2019 (week 50)
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Organization: Public Health Agency of Canada
Date published: 2019-12-20
- Influenza activity continued to increase across multiple indicators, with regions throughout the country reporting increased influenza activity.
- In week 50, the proportion of influenza B detections has increased resulting in an equal proportion of influenza A and B detections nationally. This level of influenza B activity is higher than average for this time of year and usually not seen until February or March.
- This season, the majority of hospitalizations reported by participating provinces and territories have been associated with influenza A(H3N2). Among sentinel pediatric hospitalizations with influenza, approximately 55% of cases were associated with influenza B.
- This is the last FluWatch report of the 2019 calendar year. The next FluWatch report will be published on January 10, 2020 and will include data for weeks 51-01. However, the Respiratory Virus Detection Report will be available on January 3, 2020 for weeks 51-52.
On this page
- Influenza/ILI Activity (geographic spread)
- Laboratory Confirmed Influenza Detections
- Syndromic/Influenza-like Illness Surveillance
- Influenza Outbreak Surveillance
- Severe Outcomes Influenza Surveillance
- Influenza Strain Characterizations
- Antiviral Resistance
- Vaccine Monitoring
- Provincial and International Influenza Reports
Influenza/Influenza-like Illness (ILI) Activity (geographic spread)
During week 50, both the number of regions reporting influenza activity and the level of activity reported increased compared to the previous week (Figure 1).
- Activity was reported across the country, in 11 provinces and territories.
- 74% of regions reported influenza activity; among these 72% reporting sporadic activity and 28% reported localized activity
Figure 1 – Map of influenza/ILI activity by province and territory, Canada, week 2019-50
Number of Regions Reporting in Week 50: 53 out of 53
Figure 1 - Text equivalent
|Province||Influenza Surveillance Region||Activity Level|
|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 3||No Activity|
|N.B.||Region 4||No Activity|
|N.B.||Region 5||No Activity|
|Que.||Québec et Chaudieres-Appalaches||Sporadic|
|Que.||Montréal et Laval||Sporadic|
Laboratory-Confirmed Influenza Detections
In week 50, the number of detections of influenza continued to increase, with an equal proportion of influenza A and B detections. The following results were reported from sentinel laboratories across Canada (Figures 2 and 3):
- The percentage of tests positive for influenza was 15.6%. This is similar to the average (15.3%) for week 50 over the past five seasons.
- A total of 1,272 laboratory detections of influenza were reported, of which 50.2% (638) were influenza A. The proportion of detections that are influenza B has been increasing since week 44 (October 27 to November 2), to 49.8% in week 50.
- The percentage of tests positive for influenza B (7.8%) is higher than the average (1.5%) for this time of year. The current level of influenza B activity is not normally seen until February or March.
- Among subtyped influenza A detections, a mix of A(H1N1) and A(H3N2) were detected; 60% (87 out of 145) were influenza A(H3N2).
To date this season (weeks 35 to 50), 3,762 laboratory detections of influenza were reported:
- 61% (2,291) were influenza A. The percentage of tests positive for influenza B to date this season is following a similar trend to the 2017-18 season, when influenza A and B circulated in almost equal proportions.
- Among subtyped influenza A detections (790), 68% were influenza A(H3N2).
Detailed information on age and type/subtype has been received for 3,241 laboratory-confirmed influenza cases (Table 1). To date this season (weeks 35 to 50):
- Among cases of influenza A(H3N2) (397), the largest proportion were in adults 65 years of age and older (45%).
- Cases of influenza B (1,357) were primarily in younger age groups; 63% of cases were under 20 years of age and 30% between 20 and 44 years of age.
- Among cases of influenza A(H1N1) (215), 35% of cases were in adults between 45 and 64 years of age, and 23% between 20 and 44 years of age.
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 2019-50
Number of Laboratories Reporting in Week 50: 34 out of 36
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 equivalent
|Surveillance Week||A(Unsubtyped)||A(H3N2)||A(H1N1)pdm09||Influenza B||Percent Positive A||Percent Positive B|
Figure 3 – Distribution of positive influenza specimens by type/subtype and province/territoryFootnote *, Canada, weeks 2019-35 to 2019-50
- Footnote *
Specimens from NWT, YT, and Nvt are sent to reference laboratories in other provinces.
Figure 3 - Text equivalent
|Provinces Table Figure 3 - Footnote 1||Cumulative (August 25, 2019 to December 14, 2019)|
|A Total||A(H1N1)||A(H3N2)||A(UnS)Table Figure 3 - Footnote 3||B Total||A & B Total|
|PercentageTable Figure 3 - Footnote 2||61%||11%||24%||61%||39%||100%|
|Cumulative (August 25, 2019 to December 14, 2019)|
|Influenza A||B||Influenza A and B|
|A Total||A(H1N1)||A(H3N2)||A (Un subtyped)1||Total||#||%|
Syndromic / Influenza-like Illness Surveillance
Healthcare Professionals Sentinel Syndromic Surveillance
In week 50, 1.8% of visits to healthcare professionals were due to influenza-like illness (ILI) which is slightly above 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 2019-50
Number of participants reporting in week 50: 83
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
In week 50, 3,088 participants reported to FluWatchers, of which 2.1% (65) reported symptoms of cough and fever (Figure 5).
Among the 65 participants who reported cough and fever:
- 28% consulted a healthcare professional;
- 71% reported days missed from work or school, resulting in a combined total of 108 missed days of work or school.
- 70% reported having been vaccinated for influenza this season.
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 2019-50
Number of Participants Reporting in Week 50: 3,088
Figure 5 - Text equivalent
|Surveillance Week||% cough and fever|
Online Figure – Geographic distribution of FluWatchers participants reporting cough and fever, Canada, week 2019-50
Click on the map to access the link
Influenza Outbreak Surveillance
In week 50, 14 new laboratory-confirmed outbreaks were reported: six in long term care facilities, three in an acute care facility, one in a school/daycare and four in a facility categorized as 'other', which includes facilities such as private personal care homes, correctional facilities, and colleges/universities (Figure 6). One new ILI outbreak in a school was reported.
To date this season, a total of 62 laboratory-confirmed influenza outbreaks have been reported; 33 in long-term care facilities, five in schools/daycares, nine in acute care facilities and 15 in facilities categorized as 'other'. Of the outbreaks where influenza type was reported (58), 85% (49) were due to influenza A. Among the 26 outbreaks for which the influenza A subtype was reported, 25 were associated with A(H3N2) and one was associated with A(H1N1). Four ILI outbreaks in schools/daycares have also been reported.
Figure 6 – Number of new outbreaks of laboratory-confirmed influenza by report week, Canada, weeks 2019-35 to 2019-50
Number of provinces and territories reporting in week 50: 13 out of 13
Figure 6 - Text equivalent
|Surveillance Week||Acute Care Facilities||Long Term Care Facilities||Other||Schools and Daycares||Remote and/or Isolated Communities|
Severe Outcomes Influenza Surveillance
Provincial/Territorial Influenza Hospitalizations and Deaths
To date this season, 274 influenza-associated hospitalizations were reported by participating provinces and territoriesFootnote 1.
- 69% of the cases were influenza A.
- Of the cases for which subtype was reported (164), 76% were associated with influenza A(H3N2).
- The greatest proportion of hospitalizations (40%) were among adults ≥ 65 years of age.
Thirty-one ICU admissions and three deaths have been reported.
Number of provinces and territories reporting in week 50: 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.
Pediatric Influenza Hospitalizations and Deaths
In week 50, 35 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 (29) for week 50 over the previous five seasons.
To date this season, 104 pediatric hospitalizations have been reported by the IMPACT network; 55% (57) of cases were associated with influenza B and 45 % (47) with influenza A. The largest proportion of hospitalizations (63%) were among children under 5 years of age (Figure 8).
Figure 7 – Number of pediatric (≤16 years of age) hospitalizations reported by the IMPACT network, by week, Canada, weeks 2019-35 to 2019-50
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
Figure 8 – Cumulative number of pediatric hospitalizations (≤16 years of age) with influenza by age-group reported by the IMPACT network, Canada, weeks 2019-35 to 2019-50
Figure 8 - Text equivalent
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, 38 hospitalizations and less than 5 intensive care unit admissions and deaths have been reported. The majority of hospitalizations have been due to influenza A (80%) and in adults 65 years of age and older (61%).
Influenza Strain Characterizations
From September 1 to December 19, 2019, the National Microbiology Laboratory (NML) has characterized 159 influenza viruses (78 A(H3N2), 45 A(H1N1) and 36 influenza B) that were received from Canadian laboratories.
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.
Among the 20 influenza A(H3N2) viruses antigenically characterized to date, the majority (85%) showed reduced titer by HI assay to A Kansas/14/2017 using antiserum raised against egg-propagated A Kansas/14/2017 (Figure 9a).
Nearly all (96%) of the 78 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 10).
Group 3C.2a1b viruses analysed represent:
- 85% (17 out of 20) viruses that were also antigenically characterized.
- 100% (58 out of 58) viruses which did not grow to sufficient hemagglutination titer for antigenic characterization by HI assay.
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.
Among the 45 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 9b).
A/Brisbane/02/2018 is the influenza A(H1N1) component of the 2019-20 Northern Hemisphere influenza vaccine.
Among the 36 influenza B viruses antigenically characterized this season, all belonged to the B/Victoria lineage, and the majority (78%) showed reduced titer by HI assay to B/Colorado/06/2017 using antiserum raised against cell culture-propagated B/Colorado/06/2017 (Figure 9c).
Sequence analysis showed that 96% (27) of the viruses showing reduced titre had a three amino acid deletion (162-164) in the HA gene. Sequence is pending for one isolate.
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 9 - Text Description
|Number of viruses characterized: 20|
|Antigenic phenotype of A(H3N2) virus||Number of viruses||Percentage|
|Reduced titer to A/Kansas/14/2017||17||85%|
|Number of viruses characterized: 45|
|Antigenic phenotype of A(H1N1) virus||Number of viruses||Percentage|
|Reduced titer to A/Brisbane/02/2018||0||0%|
|Number of viruses characterized: 36|
|Antigenic phenotype of influenza B virus||Number of viruses||Percentage|
|Reduced titer to B/Colorado/06/2017||28||78%|
Figure 10 - Text Description
|Number of viruses sequenced: 78|
|Genetic Clade of A(H3N2) virus||Number of viruses||Percentage|
The National Microbiology Laboratory (NML) also tests influenza viruses received from Canadian laboratories for antiviral resistance.
157 influenza viruses (74 A(H3N2), 44 A(H1N1) and 39 B) were tested for resistance to oseltamivir:
- All influenza viruses tested were sensitive to oseltamivir.
158 influenza viruses (75 A(H3N2), 44 A(H1N1) and 39 B) were tested for resistance to zanamivir:
- All influenza viruses tested were sensitive to zanamivir.
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 refers to activities related to the monitoring of influenza vaccine coverage and effectiveness.
Influenza vaccine coverage estimates for the 2019-20 season are anticipated to be available in February or March 2020.
Influenza vaccine effectiveness estimates for the 2019-20 season are anticipated to be available in February or March 2020.
Provincial and International Surveillance Links
- British Columbia – Influenza Surveillance; Vaccine Effectiveness Monitoring
- Alberta – Respiratory Virus Surveillance
- Saskatchewan – Influenza Reports
- Manitoba – Seasonal Influenza Reports
- Ontario – Ontario Respiratory Pathogen Bulletin
- Québec – Système de surveillance de la grippe (available in French only)
- New Brunswick – Influenza Surveillance Reports
- Prince Edward Island – Influenza Summary
- Nova Scotia – Respiratory Watch Report
- Newfoundland and Labrador – Surveillance and Disease Reports
- Yukon – Information on Pandemic, Influenza, Seasonal Flu, Avian Flu and H1N1
- Northwest Territories – Influenza/ Flu Information
- Nunavut – Influenza Information
- World Health Organization – FluNet (Global Influenza Surveillance Network)
- Pan American Health Organization – Influenza situation report
- U.S. Centers for Disease Prevention & Control (CDC) - Weekly Influenza Summary Update
- ECDC – Surveillance reports and disease data on seasonal influenza
- United Kingdom – Weekly Influenza Activity Reports
- Hong Kong Centre for Health Protection - Flu Express
- Australia – Influenza Surveillance Report and Activity Updates
- New Zealand – Influenza Weekly Update
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.
Ce rapport est disponible dans les deux langues officielles.
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