Case definition

In a disease outbreak investigation, a case definition is the method by which public health professionals define who is included as a case (i.e. a person considered directly affected by an outbreak). Criteria for a case definition might include a clinical test with certain characteristics, a certain biological sex, a geographic area where people must live or work, an age group, or many others. By created a case definition, public health professionals are better equipped to study an outbreak and determine possible causes. It is important to note that as investigations proceed, this definition may be expanded or narrowed. This is characteristic of the dynamic nature of outbreak investigations.