title: Circulating influenza virus, climatic factors, and acute myocardial infarction: a time series study in England and Wales and Hong Kong.
abstract: BACKGROUND
  Previous studies identifying associations between influenza and acute cardiac events may have been confounded by climatic factors. Differing seasonal patterns of influenza activity in Hong Kong and England and Wales provide a natural experiment to examine associations with myocardial infarction (MI) independent of cold weather effects.
  
  
  METHODS
  Weekly clinical and laboratory influenza surveillance data, environmental temperature and humidity data, and counts of MI-associated hospitalizations and deaths were obtained for England and Wales and for Hong Kong for the period 1998-2008. We used Poisson regression models that included environmental and seasonal variables to investigate the relationship between influenza and MI.
  
  
  RESULTS
  There were ≥1.2 million MI-associated hospitalizations and 410,204 MI-associated deaths in England and Wales, with a marked peak in the winter season. In Hong Kong, the incidence of MI, on the basis of 65,108 hospitalizations and 18,780 deaths, had a large winter and smaller summer peak, mirroring patterns of influenza activity. There was strong evidence for a link between influenza and MI both in England and Wales, where 3.1%-3.4% of MI-associated deaths (P < .001) and 0.7%-1.2% of MI-associated hospitalizations (P < .001) were attributable to influenza, and in Hong Kong, where the corresponding figures were 3.9%-5.6% (P = .018) and 3.0%-3.3% (P = .002).
  
  
  CONCLUSIONS
  Influenza was associated with an increase in MI-associated deaths and hospitalizations in 2 contrasting settings.
authors: UCL Centre for Infectious Disease Epidemiology, Research Department of Infection & Population Health, Royal Free Hospital, Rowland Hill St, London NW3 2PF, UK. c.warrengash@ucl.ac.uk
authors: Charlotte
authors: C
authors: Warren-Gash
authors: Krishnan
authors: K
authors: Bhaskaran
authors: Andrew
authors: A
authors: Hayward
authors: Gabriel M
authors: GM
authors: Leung
authors: Su-Vui
authors: SV
authors: Lo
authors: Chit-Ming
authors: CM
authors: Wong
authors: Joanna
authors: J
authors: Ellis
authors: Richard
authors: R
authors: Pebody
authors: Liam
authors: L
authors: Smeeth
authors: Benjamin J
authors: BJ
authors: Cowling
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