, Ruth Lynfield, Mary Lou Lindegren, Joseph Bresee, and Lyn Finelli
Figure 1. Population-based influenza hospitalization surveillance case ascertainment and review process, Influenza Hospitalization Surveillance Network, United States. Core data transmitted weekly to the Centers for Disease Control and Prevention (CDC) are patient identification number, surveillance site, hospital admission date, patient’s date of birth, type of influenza test, and type of influenza virus. Case finding and chart reviews are done manually.