Abstract
ObjectivesWe aim to document and analyze influenza hospitalization burden in light of antigenic changes in circulating influenza viruses in Hong Kong.MethodsThe pediatric age-specific rates of influenza A hospitalization in Hong Kong for 2004–2011 which encompassed the emergence of H1N1pdm09 were extrapolated from admissions to 2 hospitals that together catered for 72.5% of all pediatric admissions on Hong Kong Island. Influenza A was detected by immunofluorescence, culture and/or PCR on nasopharyngeal aspirates.ResultsInfluenza A caused high rates of hospitalization in children with year to year fluctuations. The highest hospitalization burden was seen with H1N1pdm09 in 2009. Additional factors affecting hospitalization were the proportion of viral circulation among different subtypes, and antigenic drifts. Taking these into effect, an H3N2 dominated year was not always associated with more hospitalizations than a ‘seasonal’ H1N1 year. Hospitalization burden was higher in seasons when drifted viruses of H1N1 or H3N2 dominated. No hospitalization was documented in infants <6 months of age during years when an undrifted virus circulated (2006 for H1N1 and 2008 for H3N2) but significant hospitalization was observed with a drifted or shifted virus (2004, 2005, 2007 and 2010 for H3N2, and 2009 for H1N1pdm09).ConclusionsWe documented a consistently high pediatric hospitalization burden of influenza A. Knowledge of antigenic changes and their proportion of circulation aids in the interpretation of impact of the subtypes. Year-to-year variation in hospitalization rates in young infants appeared to correlate with antigenic variation, lending support to the role of protection from maternal antibodies.
Highlights
Influenza leads to a significant burden of hospitalization in children annually
The first case of H1N1pdm09 in Hong Kong was diagnosed on 1 May 2009 in a traveler from Mexico arriving in Hong Kong [18]
From until the end of June 2009, Hong Kong implemented a containment strategy where all patients confirmed to be infected with H1N1pdm09 were hospitalized and discharged according to isolation and infection control measures, regardless of clinical indication
Summary
Influenza leads to a significant burden of hospitalization in children annually. Influenza disease and hospitalization are the outcome of dynamic interaction between the virus and the susceptible hosts in the population. In order to truly gain insight into the impact of influenza hospitalization, the data should be interpreted in light of the subtypes and antigenic drifts and even shift. These data are lacking in the literature. We seek to compare the agespecific hospitalization disease burden of influenza A in children in
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