Using NORS Data

Most outbreaks in the United States are investigated by state, local, and territorial health departments. Outbreak information is then voluntarily reported to CDC by the public health agency that conducted the investigation. CDC may assist with outbreak investigations that involve more than one state, outbreaks that are particularly large, or for which the state or local health department requests assistance. The current reporting forms can be found on Forms & Guidance.

Foodborne and waterborne disease outbreaks have been reported to CDC since the 1970s. Reporting was expanded in 2009 to include all enteric disease outbreaks, regardless of mode of transmission. The table below provides an overview of the types of outbreak data and the periods when the data were collected.

Years Active
Mode of Transmission 1973—1997 1998—2008 2009—Present
Foodborne (FDOSS*) pFORS*
(paper form)
(electronic reporting)
(electronic reporting)
Waterborne (WBDOSS*) Paper form (began 1971) NORS
Person-to-person No systematic reporting NORS
Animal Contact No systematic reporting NORS
Environmental No systematic reporting NORS
Indeterminate/Unknown No systematic reporting NORS

*FDOSS: Foodborne Disease Outbreak Surveillance System; pFORS: paper-based Foodborne Disease Outbreak Reporting System; eFORS: electronic-based Foodborne Disease Outbreak Reporting System; NORS: National Outbreak Reporting System; WBDOSS: Waterborne Disease and Outbreak Surveillance System

Note: In addition to these basic differences among the reporting systems, each system collected different information in different formats. Not all information was collected consistently across systems and years, so caution is advised when combining data.

CDC epidemiologists routinely perform data quality and assurance procedures before summarizing and publishing data. This process is referred to as “close-out.” Final data are typically available for release 12–18 months after the end of the reporting year; this allows states time to finalize reports and CDC time to perform close-out. NORS is a dynamic system, and reports can be modified when new information is available, even months or years after data have been closed out.

Outbreak Data Are Reported to NORS and Summarized by CDC

The general flow of outbreak information to NORS: 1) People are exposed to a pathogen; 2) People get sick and seek treatment 3) Health department is notified of a possible outbreak; 4) Health department conducts an outbreak investigation; 5) Health department enters outbreak information into NORS; 6) CDC checks data for accuracy and analyzes; 7) Data are summarized and published.

An outbreak reported to NORS is defined as the occurrence of two or more cases of a similar illness resulting from a common exposure. Data on specific reports might not be released if:

  • the report does not meet the definition of an outbreak (e.g., only contains information on a single case of illness)
  • the report has not been finalized by the state that reported it or has not been closed-out by CDC
  • Reporting of outbreaks to CDC is voluntary; outbreaks are likely underreported due to limited resources and training in health departments, which might vary by outbreak mode of transmission.
  • Only a small proportion of illnesses reported each year are identified as associated with outbreaks. The extent to which the distribution of various sources and settings implicated in outbreaks reflects the same sources of infection and settings of sporadic illnesses is unknown.
  • Outbreaks occurring on cruise ships with international ports of call and those where the exposure occurred outside the United States are not reported through NORS. For more information on cruise ship outbreaks, please visit the CDC’s Vessel Sanitation Program.
  • Additional limitations may apply to the content or use of outbreak surveillance datasets.
  • NORS Dashboard — Use this web-based platform to search and download nearly 20 years of outbreak information on foodborne, waterborne, and other enteric disease outbreaks reported to CDC.
  • Waterborne disease and outbreak surveillance reports — Find published line lists of waterborne disease outbreaks dating from 1971 through the most recent year of published data.
  • Foodborne disease outbreak reports — See summaries of foodborne disease outbreaks from 1966 through the most recent year of published data.
  • Data request — Obtain additional data — including data for use in scientific publications — by emailing the NORS Dashboard mailbox.
Page last reviewed: November 4, 2019