Influenza-associated mortality in Hong Kong

Background. The impact of influenza on mortality in countries in subtropical and tropical regions is poorly quantified. Estimation of influenza-related illness in warm-climate regions is more difficult, because the seasonality of virus circulation is less well-defined. Partly as a result of these factors, influenza vaccine is grossly underutilized in the tropics, even for individuals greater than or equal to 65 years of age. Methods. Weekly numbers of deaths were modeled by Poisson regression, and excess deaths attributable to influenza in Hong Kong were estimated for 1996 - 1999. Comparison of weekly mortality during periods of influenza predominance and periods of low influenza activity was used to derive an alternative estimate of influenza-associated mortality. Results. Estimates derived from the Poisson model indicated that influenza resulted in 7.3 deaths per 100,000 population per year ( 95% confidence interval [CI], 3.1 - 11.4) from cardiorespiratory disease among individuals aged 40 - 65 years and 102.0 deaths per 100,000 per population per year ( 95% CI, 61.2 - 142.7) among individuals aged greater than or equal to 65 years. Although respiratory diseases accounted for the majority of influenza-related deaths, influenza also contributed to 13.8% ( 95% CI, 4.8% - 22.7%) and 5.3% ( 95% CI, 1.2% - 9.3%) of deaths related to ischemic heart disease. Conclusion. Influenza is associated with deaths due to ischemic heart disease as well from respiratory diseases. Overall influenza-associated mortality in a region with a warm climate, such as Hong Kong, is comparable with that documented in temperate regions. The need for influenza vaccination in tropical regions needs to be reassessed.