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    Public Health Agency of Canada (PHAC)
Canada Communicable Disease Report

Volume 27-05
1 March 2001

[Table of Contents]

 

 

RESPIRATORY VIRUS SURVEILLANCE
FLUWATCH PROJECT UPDATE


Introduction

Canada's national influenza surveillance system, the FluWatch program, is now in it's fifth year. The program collects data on influenza-like illness (ILI) and monitors the types of influenza virus circulating in the population to provide a national picture of influenza activity. FluWatch also reports institutional outbreaks and contributes to international surveillance activities. This article provides a brief summary of the current season from 1 October, 2000 up to and including 27 January, 2001.


Methods

FluWatch reports include data and information from four main sources: (1) laboratory reports of positive influenza tests in Canada; (2) sentinel physician reporting of ILI; (3) provincial/territorial assessment of influenza activity levels based on various indicators, including laboratory surveillance, ILI reporting, outbreaks and other community indicators; (4) international surveillance system reports of influenza activity (CDC, European Influenza Surveillance System [EISS], WHO).


Results

Across Canada, 28 laboratories submit respiratory virus detection data on a weekly basis to the Centre for Infectious Disease Prevention and Control (CIDPC). Since 27 August, 2000, CIDPC has received reports on 23,552 tests for influenza, of which 1,372 (5.8%) tested positive for influenza viruses: 191 (13.9%) for influenza A and 1181 (86.1%) for influenza B. The provincial distribution of positive tests is as follows: Newfoundland (2), Prince Edward Island (0), Nova Scotia (37), New Brunswick (13), Quebec (34), Ontario (60), Manitoba (69), Saskatchewan (432), Alberta (521) and British Columbia (204). Influenza B has been isolated in all but one province and influenza A in all but the Atlantic provinces. To-date, 140 influenza isolates have been characterised by the National Microbiology Laboratory: 36 were A/New Caledonia/20/99-like (H1N1); two were A/Panama/2007/99-like, and; 102 were B/Yamanashi/166/98-like. All of the strains characterised to date are covered by the 2000-2001 vaccine.

Weekly ILI rates, reported through the sentinel system, have remained at or below baseline since the beginning of the season. Figure 1 shows the Canadian age-standardized, census-division weighted ILI rates for the current season compared to the mean rate with 95% confidence intervals for the previous 4 years of the FluWatch program. Figure 2 shows the cumulative ILI rates ([Sigma reported ILI cases/Sigma reported patient visits] × 1,000) for each province since 1 October, 2000. Manitoba and the North West Territories have the highest cumulative ILI rates this season, while Prince Edward Island, British Columbia and Alberta have the lowest cumulative ILI rates. Up to end of 2000, the season had been relatively mild with mostly sporadic activity occurring across Canada and only limited localised activity in southern Alberta and Saskatchewan during late December. The first widespread influenza activity occurred in the Yukon, between 24 December, 2000 and 6 January, 2001 and in Saskatchewan between 24 December, 2000 and 20 January, 2001. By 27 January (week four), widespread activity was limited to one region (Prince Edward Island). Figure 3 shows the number of influenza surveillance regions reporting localized and widespread influenza activity by report week.
Figure 1
Census-Division weighted age-standardized ILI* rates, Canada, by report week for the 2000/2001 influenza season compared to 1996/1997 through 1999/2000 seasons (mean rate with 95% confidence intervals)
Census-Division weighted age-standardized ILI rates

Figure 2
Cumulative ILI* rates per 1,000 patient visits ([Sigma reported ILI cases/Sigma reported patient visits] × 1,000) for each province since 1 October, 2000
Cumulative ILI rates for each province
* influenza-like illness

Figure 3
Number of influenza surveillance regions † reporting widespread or localized influenza activity, Canada, by report week, 2000-2001 (n = 53)
Number of influenza surveillance regions reporting widespread or localized influenza activity
† Sub-regions within the province or territory as defined by the provincial/territorial epidemiologist.

   

The USA is also experiencing a fairly mild season. The proportion of overall patient visits for ILI has remained within baseline at 1% to 3% and the proportion of deaths due to pneumonia and influenza (7.9%) has remained below the epidemic threshold throughout the current season. Since the beginning of October, 2000, a total of 2,239 influenza isolates have been reported; 1,640 (73%) were influenza A (97% H1N1 and 3% H3N2) and 599 (27%) were influenza B. Influenza A viruses have predominated in six regions (East North Central, Mountain, New England, South Atlantic, West North Central, and West South Central) whereas influenza B viruses have predominated in two regions (Mid-Atlantic and Pacific). One other region (East South Central) has had approximately equal numbers of influenza A and B isolates. Of the 153 influenza viruses that have been characterised to date, 114 (74.5%) were influenza were A/New Caledonia/20/99-like (H1N1), eight (5%) were A/Bayern/07/95-like (H1N1)*, 10 (6.5%) were A/Panama/2007/99-like (H3N2) and 21 (14%) were influenza B/Beijing/184/93-like.

On a global level, the WHO reported regional influenza activity in Canada and parts of Europe during the months of December, 2000 and January, 2001. Widespread activity was first reported for the Eastern Mediterranean during December, 2000. In the week of 21 to 26 January, 2001, widespread activity was reported for Germany, Czech Republic and Slovak Republic. Of the viruses sub-typed thus far, the predominant types have been influenza A (H1N1 predominates the characterized strains) in the United States and Europe and influenza B in Canada(1-3).

FluWatch reports are published weekly (October to April) and can be accessed through Health Canada's FluWatch website: <http://www.phac-aspc.gc.ca/fluwatch/index.html>.

Please note that the above graphs may change as late returns come in.


References

  1. Centers for Disease Control and Prevention. Influenza summary update, Week ending January 27, 2001-Week 04. URL:
    <http://www.cdc.gov/ncidod/diseases/flu/weeklychoice.htm>.

  2. World Health Organisation, FluNet. Isolates/activity, ILI activity, 21/01/01 to 27/01/01, World. URL: <http://www.who.int/GlobalAtlas/home.asp>.

  3. European Influenza Surveillance System. Weekly Electronic Bulletin, 01/02/2001: Week 4, Issue Number 17. URL: <http://www.eiss.org/cgi-files/bulletin.cgi>.

Source:  JF Macey, MA, MSc, Field Epidemiology Training Program, Centre for Surveillance Coordination and Division of Respiratory Diseases, Bureau of Infectious Diseases, B Winchester, BSc, MSc, SG Squires, MSc, T Tam, MD, Division of Respiratory Diseases, P Zabchuk, Division of Disease Surveillance, Bureau of Infectious Diseases, Centre for Infectious Disease Prevention and Control, Ottawa; M Vanderkloot, Bureau of Operations Planning and Policy, Strategic Policy Directorate, Public Health Agency of Canada, Ottawa, Ontario; Y Li, PhD, National Microbiology Laboratory, Winnipeg, Manitoba.

* The CDC reports that although A/Bayern-like viruses are antigenically distinct from the A/New Caledonia-like viruses, the A/New Caledonia/20/99-like vaccine strain produces high titres of antibody that cross-react with A/Bayern/07/95-like viruses(1).

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