Influenza-related deaths and hospitalizations in Hong Kong: a subtropical area

While influenza vaccination has been widely used in developed countries to reduce mortality and morbidity in high-risk populations, the lack of regional data on the health burden of influenza and the uncertainty of the applicability of data from temperate areas have been major impediments to establishing an evidence-based policy on the wider use of influenza vaccine in tropical and subtropical regions of the world.

The aim of this study was to estimate the annual excess deaths and hospitalizations related to influenza in the Hong Kong Special Administrative Region (HKSAR) for the years 1999 and 2000.

Correlation and regression models were used to estimate the excess deaths and hospitalizations related to influenza in the general population of HKSAR for the years 1999 and 2000, using routinely collected mortality and hospitalization data, and virological laboratory data collected by the HKSAR Influenza Surveillance System.

The annual mean excess numbers of deaths related to influenza in Hong Kong were estimated to be 613 for pneumonia and influenza, and 2302 for respiratory and circulatory diseases. The mean excess numbers of hospitalizations attributable to influenza were 4051 for pneumonia and influenza, and 15,873 for respiratory and circulatory diseases. The crude influenza-related mortality and hospitalization rates in Hong Kong, a subtropical area, exceeded those documented in temperate regions.

The finding of significant mortality and morbidity related to influenza in a subtropical area is in accordance with the results of previous studies in tropical and subtropical regions. This simple methodology can be used for the development of influenza immunization policy in many developing countries in tropical and subtropical regions. The enormous potential of influenza vaccination in saving lives and reducing suffering warrants serious consideration of the expanded use of influenza vaccine in tropical and subtropical regions.