Hospitalization risk of the 2009 H1N1 pandemic cases in Hong Kong
1 School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
2 Department of Microbiology, The University of Hong Kong, Hong Kong Special Administrative Region, People’s Republic of China
3 HKU-Pasteur Center, Hong Kong Special Administrative Region, People’s Republic of China
4 Squina International Centre for Infection Control, School of Nursing, The Hong Kong Polytechnic University, Hong Kong Special Administrative Region, People’s Republic of China
5 5/F William Mong Block, 21 Sassoon Road, Pokfulam, Hong Kong Special Administrative Region
BMC Infectious Diseases 2014, 14:32 doi:10.1186/1471-2334-14-32Published: 16 January 2014
Reliable assessment for the severity of the 2009 H1N1 pandemic influenza is critical for evaluation of vaccination strategies for future pandemics. This study aims to estimate the age-specific hospitalization risks of the 2009 pandemic cases during the first wave in Hong Kong, by combining the findings from the serology and disease burden studies.
Excess hospitalization rates associated with the pandemic H1N1 were estimated from Poisson regression models fitted to weekly total numbers of non-accidental hospitalization from 2005 to 2010. Age-specific infection-hospitalization risks were calculated as excess hospitalization rates divided by the attack rates in the corresponding age group, which were estimated from serology studies previously conducted in Hong Kong.
Excess hospitalization rate associated with pandemic H1N1 was highest in the 0–4 age group (881.3 per 100,000 population), followed by the 5–14, 60+, 15–29, 50–59, 30–39 and 40–49 age groups. The hospitalization risk of the infected cases (i.e. infection-hospitalization risk) was found highest in the 60+ age group and lowest in the 15–29 age group, with the estimates of 17.5% and 0.7%, respectively.
People aged 60 or over had a relatively high infection-hospitalization risk during the first wave of the 2009 H1N1 pandemic, despite of a low attack rate in this age group. The findings support the policy of listing older people as the priority group for pandemic vaccination.