Cases will be obtained from children who are enrolled in active surveillance for acute gastroenteritis being conducted at the two initial surveillance sites. These sites include: Cincinnati Children's Hospital Medical Center (2009-2012) and the Medical University of South Carolina (2009-2012). Cases and controls will be identified retrospectively for the 2008-2011 seasons and prospectively through active surveillance for the 2011-2012 season. The active surveillance programs conduct prospective surveillance for hospitalizations and ED visits due to AGE (acute gastroenteritis) in children < 6 years of age. Even though Rotarix was commercially available on January 1, 2008, the actual date that RV1 was initially used varied across sites. The date that Rotarix was initially used will be determined for each site through examination of the data. Children with laboratory-confirmed rotavirus infection (bulk stool sample positive for rotavirus using a rotavirus EIA) will be included as a case if they were born 2 months prior to the initial date of Rotarix availability at each site. The vaccine record for each case will be obtained to determine the vaccine status of the child.