Affiliation: | 1. Department of Family Medicine, University of Pittsburgh School of Medicine, , Pittsburgh, PA, USA;2. Department of Pathology, University of Pittsburgh School of Medicine, , Pittsburgh, PA, USA;3. Department of Infectious Disease and Microbiology, University of Pittsburgh Graduate School of Public Health, , Pittsburgh, PA, USA;4. Department Epidemiology, University of Pittsburgh Graduate School of Public Health, , Pittsburgh, PA, USA;5. Influenza Division, Centers for Disease Control and Prevention, , Atlanta, GA, USA |