A notifiable condition is one which, when identified, legally requires health providers and laboratories to report the case to local and/or state health departments. Those health departments may then voluntarily report the cases to the CDC, which they typically do. The CDC’s National Center for Health Statistics hosts the National Notifiable Diseases Surveillance System (NNDSS), which collects data on notifiable diseases from all 50 states, Washington D.C., and five U.S. territories.
How a disease is reported depends on its case definition, which can be “confirmed,” “probably,” or “suspected.” The list of diseases that qualify as notifiable varies by year and can be searched by year at this CDC tool. The list as of 2025 is approximately 100 diseases. While being notifiable increases the reliability of surveillance of a particular disease, plenty of limitations remain for national surveillance of notifiable diseases. Reporting from local, state and territory jurisdictions is voluntary, and cases are only reported if they are identified according to their official case definition.