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, and in 2023 to include reporting of certain fungal disease outbreaks. The table below provides an overview of the types of outbreak data and the periods when the data were collected.
|Mode of Transmission||1973—1997||1998—2008||2009—Present|
|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
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.
- NORS outbreaks (all modes)
- NORS Relational Data Dictionary [1 sheet] (Updated January 2023) — A complete list of variables contained in the CDC 52.14 form and downloadable by NORS users in a relational format
- NORS Flat Data Dictionary [1 sheet] (Updated January 2023) — A complete list of variables contained in the CDC 52.14 form and downloadable by NORS users in a flat format