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Estimates of flu-related deaths rise with new statistical models

CMAJ

A US study has determined that more people are dying of influenza than previously thought, and the finding holds true for Canada too.

The study (JAMA 2002;289[2]:179-86), funded by the US Centers for Disease Control (CDC), used a new statistical model to estimate that 36 000 Americans are dying from influenza-related complications each year. The previous estimate was 20 000 deaths. An additional 11 000 mostly elderly people die annually from respiratory syncytial virus (RSV).

The estimates are "similar in Canada," says Dr. Theresa Tam, chief of respiratory disease with the Centre for Infectious Disease Prevention and Control. Canada's flu toll had been estimated at 500 to 1500 deaths annually, but after using new modelling Health Canada estimated that 700 to 2500 deaths may be attributable to influenza.

Health Canada takes the total number of deaths related to pneumonia and influenza and uses various techniques to determine how many deaths can be attributed to flu. The newer statistical models, which are similar to those used by the CDC, incorporate laboratory identifications for influenza and RSV, says Tam.

Statistics Canada says the number of deaths from pneumonia and influenza has increased from approximately 4200 in 1979 to 8030 in 1997. Of the latter, 6618 cases involved people older than 75, compared with 2965 in 1979. Despite the increase in the absolute number of deaths, says Tam, mortality rates have actually gone down in every age group. "Canada now ranks number 1 in the world for influenza [vaccine] doses per capita," says Tam. "It's almost 1 in 3."

Tam says every province has tried to increase this immunization coverage. "As a public health message, it's worth concentrating on. It still prevents hospitalizations and deaths."

So should every province follow the lead of Ontario, which offers universal immunization against influenza? "That's a very good question," says Dr. Michael Tarrant, who represents the College of Family Physicians of Canada on the Canadian Coalition for Influenza Immunization. "Everyone is awaiting the results of Ontario's experiment. It's expensive but it may be worth while." (The vaccine costs $5 per person plus $10 to $15 to administer.)

The CDC attributes the larger number of deaths in the US to an aging population and to the "predominance of influenza A (H2N2) viruses, the most virulent of the recently circulating influenza viruses." — Barbara Sibbald, CMAJ

This Article Full Text (PDF) Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Sibbald, B. Search for Related Content PubMed PubMed Citation Articles by Sibbald, B. Related Collections Influenza

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Copyright 1995-2003, Canadian Medical Association. All rights reserved. ISSN 1488-2329 (e) 0820-3946 (p) All editorial matter in CMAJ represents the opinions of the authors and not necessarily those of the Canadian Medical Association.