The focus of a public health intervention is to prevent rather than treat a disease through surveillance of cases and the promotion of healthy behaviors. In addition to these activities, in many cases treating a disease can be vital to preventing it in others, such as during an outbreak of an infectious disease. Vaccination programs and safe water supply are examples of public health measures. Many diseases are preventable through simple, non-medical methods. Public health plays a very important role in prevention efforts in the developing world, either through the local health system or through international non-governmental organizations (NGOS).