Abstract
Seasonal influenza is known to spread within and among educational organizations. Detailed understanding of the pattern of infection requires prospective epidemiological studies among all schools in a community. This prospective survey evaluated 13,217 schoolchildren attending all 29 public elementary schools in Matsumoto City, Japan, in 2014/2015. Questionnaires were distributed to school nurses to obtain information about onset date and suspected route of transmission of influenza of all schoolchildren diagnosed at medical institutions. Responses were obtained regarding 2,548 infected individuals, representing 96% of those reported. Epidemic curves were drawn for each school and the numbers of individuals calculated. Distance between schools was not associated with influenza spread over time. However, modeling showed that the occurrence of initial infection at each school and its spread over time could be fitted with a logistic curve. The transmission route for most children initially infected at each school was through a member of their households, whereas the route for most remaining schoolchildren was through the school. These findings indicate that seasonal influenza was initially transmitted to schoolchildren by household members and then spread throughout the schools, with the initially infected child at each school fitting logistic curves over time.
