The planned epidemiology study will be conducted in IMSS hospitals and potentially use the IMSS database to re-capture potential cases of IS and fatal cases and as a source of matched case controls. The purpose of this project is to complement this data link system with an active surveillance system for IS - in order to assess the feasibility of using the IMSS data system by generating results that provide scientific validity. Such comprehensive (passive and active) surveillance systems will facilitate the post licensure safety profile evaluation of vaccines such as a vaccine against rotavirus diarrhoea.