There are many factors that play a role in the origin of disease, these factors include such as water pollution, air pollution, food contamination and sanitation. Such factors can be controlled if the community takes preventive measure in ensuring clean water air and sanitation, so at individual level the disease don't occur and also there are many communicable disease which are transmitted from person to person so if the community is healthy there is less chance of communicable disease. Therefore you can understand that community health is essential for individual health.