As a part of its mission to control communicable diseases, public health authorities in each state establish requirements that providers must report each case that presents with certain conditions. The purpose is to stem the spread of disease by contacting people who have been exposed to the reported “index” case and taking preventive action.
The National Notifiable Diseases Surveillance System traces its history to legislation which in 1878 authorized the U.S. Marine Hospital Service (i.e., the forerunner of the Public Health Service [PHS]) to collect reports on the incidence of cholera, smallpox, plague, and yellow fever. The system has evolved to one that relies on federal state cooperation in the definition of conditions that the states require health care providers to report.
Reportable conditions include infectious diseases such as sexually transmitted conditions, those with a high potential for serious consequences and new conditions requiring special public health measures.
A full list of these conditions and their definitions can be found on this website at CDC.