Abstract
Reliable estimates of the morbidity burden caused by the 2009 pandemic influenza (pH1N1) are important for assessing the severity of the pandemic. Poisson regression models were fitted to weekly numbers of cause-specific hospitalisation in Hong Kong from 2005 to 2010. Excess hospitalisation associated with the 2009 pandemic and seasonal influenza was derived from the model by incorporating the proxy variables of weekly proportions of specimens positive for the pandemic influenza A(H1N1)pdm09, seasonal influenza A (subtypes H3N2 and H1N1) and B viruses. Compared with seasonal influenza, pH1N1 influenza was associated with higher hospitalisation rates for acute respiratory disease (ARD) among children younger than 18 years and adults aged between 18 and 64 years, but among the elderly aged 65 years and older the hospitalisation rates were lower for pH1N1 than for seasonal H3N2 and H1N1 influenza. Hospitalisation rates for chronic diseases associated with pH1N1 influenza were generally higher than those associated with seasonal influenza. The reported hospitalised cases with laboratory-confirmed pandemic infections accounted for only 16% of pH1N1 influenza-associated hospitalisations for ARD in the age group 75 years and older, and 5‒66% of hospitalisations for chronic diseases in those older than 40 years. The 2009 H1N1 influenza pandemic was associated with a dramatically increased risk of hospitalisation among children and young adults. The morbidity burden of pandemic was underreported in old people and in those with chronic conditions.
Highlights
In April 2009 a novel influenza A(H1N1) virus of swineorigin emerged and quickly spread worldwide [1]
Presanis and colleagues estimated that only 20‒30% of hospitalised pH1N1 cases in the United Kingdom confirmed by the laboratory surveillance during the 2009 pandemic [22]
In the present study we used a Poisson regression model, which has been widely adopted for estimation of the influenza disease burden [23,24,25], to assess excess hospitalisation associated with seasonal influenza
Summary
In April 2009 a novel influenza A(H1N1) virus of swineorigin (referred to as pH1N1 hereafter) emerged and quickly spread worldwide [1]. Previous studies have reported that annual hospitalisation rates with laboratory-confirmed pandemic infections ranged from 3 to 110 per 100,000 person-years [2,3,4]. It is likely that these rates seriously underestimated the true burden of the pandemic, as many cases were not tested for pandemic infections due to limited laboratory capacity [5]. The tests could have been biased towards children and young adults in whom the pH1N1 infection rates were reported to be higher, but severe outcomes after infections were more likely to occur in the elderly aged 65 years or older [6,7]. Previous studies have further found that few pandemic-associated fatalities in persons older than 65 years were captured by intensive laboratory tests [8,9]. We and others have demonstrated that excess hospitalisation estimated from Poisson models can provide reliable estimates for true morbidity burden of seasonal influenza [10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
