The SMART² study aims to improve the understanding of how influenza, and other respiratory viruses, spread between school children and the community. Using a mix of school-based and cohort surveillance, we hope to provide information on the conduct of optimal surveillance in scchool-based populations to improve prediction of influenza activity in the community. We will use traditional time series modeling approaches and Hidden Markov Models to model the temporal dynamics of influenza activity in the community as a function of cause-specific school absence and other covariates. We will also use these models to predict the future course of influenza in the school-aged population as a function of cause specific school absences in earlier time periods. Surveillance is conducted in the Pittsburgh metropolitan area in close collaboration with staff at the University of Pittsburgh.