Older Age and a Reduced Likelihood of 2009 H1N1 Virus Infection

Abstract

Early epidemiologic reports regarding the 2009 pandemic influenza A (H1N1) virus suggest that cases of infection and deaths are concentrated in adults between the ages of 20 and 40 years.¹ This finding could reflect age-related differences in susceptibility or differential testing and diagnosis in this age group. Increased susceptibility to infection in young persons is characteristic of influenza pandemics and has important implications for disease-control policy.² We examined whether the reported excess of cases in younger persons derives from testing practices or reflects a differential risk of infection in Ontario, Canada.