In medicine, the ongoing evaluation of an individual who has an increased risk of developing a disease or who has a disease that appears to be clinically stable or not progressing. Surveillance is also used to find early signs that a disease has come back. In public health, surveillance may also refer to the ongoing systematic collection and analysis of information about the incidence, prevalence, morbidity, survival, and mortality related to a disease or health-related event in a certain group of people.