Gerardo Chowell and coworkers report the incidence of pandemic influenza H1N1 morbidity and mortality in 32 Mexican states in 2009 and quantify the association between local influenza transmission rates, school cycles, and demographic factors. By using the epidemiological surveillance system of the Mexican Institute for Social Security, which covers about 40% of the Mexican population (107 million individuals), they compiled age- and state-specific rates of incident influenza-like illness and pandemic H1N1 influenza cases by day of symptom onset to analyze the geographic patterns of the dissemination of the flu pandemic across Mexico in 2009. Using these data as inputs to a mathematical model they show that the age distribution of pandemic influenza morbidity was greater in younger age groups while the risk of severe disease was highest in older age groups. But most importantly, these findings support the effectiveness of early mitigation efforts including mandatory school closures and cancellation of large public gatherings, reinforcing the importance of school cycles in the transmission of pandemic influenza.
Source: Public Library of Science