Excess hospital admissions for pneumonia, chronic obstructive pulmonary disease, and heart failure during influenza seasons in Hong Kong

It is widely held that Southern China is a hypothetical influenza epicentre for the emergence of pandemic influenza viruses. However, influenza is perceived as a relatively unimportant infection in this part of the world compared with western countries. Hong Kong is situated within the hypothetical epicentre and serves as a sentinel post for the region. In a retrospective study, the influenza-associated excess hospitalisations in a regional hospital for pneumonia, chronic obstructive pulmonary disease (COPD), heart failure, and asthma in persons aged > or = 65 years from 1998 to 2001 were each estimated by a model taking into consideration the confounding effect of other respiratory viral infections, seasonal factors, time trends, and weather and pollution indices. In the regression models, influenza activity is an independent significant factor affecting admission rates for pneumonia, COPD, and heart failure but not that for asthma. The variations in hospital admissions for pneumonia, COPD, and heart failure explained by influenza activity were 38.9, 7.5, and 45.6%, respectively. The adjusted rates of excess influenza-associated hospital admissions for the three diagnoses combined amounted to 58.5, 20.0, 29.2, and 13.4 per 10,000 populations aged > or = 65 years in 1998, 1999, 2000, and 2001, respectively. In conclusion, influenza activity is associated significant excess hospital admissions among elderly aged 65 or above in Hong Kong, comparable to the data reported in Western countries. The findings support a wider application of annual influenza vaccination in this region.