Abstract
Elementary schools are thought to be amplifiers for infections in influenza epidemics in communities, considering the poorer immunity against the disease among school children, compared with the adult population, and the high activity and communal school life. Therefore, infection control in schools might be one of the key issues for mitigation of influenza endemics in communities. However, little information has been available on the dynamics of influenza transmission among school children or introduction of the disease into schools. In this study, we analyzed the incidence profiles of A(H1N1) pdm09 pandemic influenza in Shimo-miito elementary school, Meiwa-cho, Mie, Japan, from October 2009 to January 2010, where 49.1% children developed influenza during the estimated epidemic period of 79 days. The mean incidence rate was 1.01 cases a day. New cases were detected in 43.0% of days during the period, 80.0% of days with less than three cases, and only 13.3% with more than 5 new cases, suggesting that the epidemic in the school was gradual and intermittent rather than rapid and explosive. We estimated the possible infection linkages among the children by analyzing the relationships between the onset day and the incubation period, under the presumption that infected children could be the source of infection within 24 hours before the onset day. The results indicated that the source of infection for 50.0-66.7% of cases was inside the same class, showing that 33.4-50.0% of children who develop influenza might be infected through other routes. Most of the infection linkages in classes were found to be terminate rapidly. Repeated new emergences and terminations of infection linkages was the typical pattern of the influenza epidemic in this elementary school in 2009.
