Abstract
BackgroundReliable 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.MethodsExcess 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.ResultsExcess 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.ConclusionsPeople 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.
Highlights
Reliable assessment for the severity of the 2009 H1N1 pandemic influenza is critical for evaluation of vaccination strategies for future pandemics
Model derived excess hospitalization is believed to capture both laboratory confirmed influenza hospitalized cases and those who were not laboratory diagnosed [6]. We used this estimate of A(H1N1) pdm09-associated excess hospitalization as the numerator and the estimate of A(H1N1)pdm09 infected cases from the previous serological studies as the denominator [4,5], to calculate the infection-excess hospitalization risk of the 2009 H1N1 pandemic in Hong Kong
Significant association of A(H1N1)pdm09 with hospitalization was only found in the age groups below 30 years old (p < 0.05)
Summary
Reliable assessment for the severity of the 2009 H1N1 pandemic influenza is critical for evaluation of vaccination strategies for future pandemics. Obtaining a reliable estimate for IHR remains challenging, because infected cases might have not shown any symptoms or not been differentiated from other respiratory infections. Model derived excess hospitalization is believed to capture both laboratory confirmed influenza hospitalized cases and those who were not laboratory diagnosed [6] We used this estimate of A(H1N1) pdm09-associated excess hospitalization as the numerator and the estimate of A(H1N1)pdm infected cases from the previous serological studies as the denominator [4,5], to calculate the infection-excess hospitalization risk (eIHR) of the 2009 H1N1 pandemic in Hong Kong
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