DESCRIPTION (provided by applicant): The burden of disease related to influenza virus infection in India is not well defined but likely to be substantial given that India accounts for 20% of global childhood deaths due to acute respiratory infections. To address this issue a population-based longitudinal burden of disease study will be implemented at two study sites in rural India. Vadu is the proposed southern Indian study site located 40 Km northeast of Pune and Ballabhgarh is the proposed northern Indian study site located 40 Km south of Delhi. Each of these sites have ongoing community and demographic surveillance systems that make them optimal locations for study implementation. The primary aim of this study is to determine the incidence of severe hospitalized and medically attended non-hospitalized influenza in each of these communities. Secondary aims include describing the spectrum and seasonality of clinical illness related to seasonal influenza, identifying risk factors for severe seasonal influenza, and describing health care utilization and the burden of respiratory disease that should seek medical care but does not, in these communities. After approvals have been obtained and the study is initiated, implementation and analysis is expected to take approximately three years.