Reporting and Classification
Outbreaks associated with drinking water, recreational water and other water exposures are reported to the Waterborne Disease and Outbreak Surveillance System (WBDOSS) through the National Outbreak Reporting System (NORS). Waterborne disease outbreak reports include these items:
- Characteristics of the outbreak (for example, number of cases, timing of outbreak, and location)
- Results from epidemiologic and environmental health investigations
- Results from clinical specimen and environmental water sample testing
Data Sources
Jurisdictional health authorities such as states and territories report information about outbreaks through the National Outbreak Reporting System (NORS).
Forms
Waterborne disease outbreaks investigated by local public health agencies are reported to the state, territorial, or Freely Associated State public health agency. State agencies and other reporting jurisdictions can report waterborne disease outbreaks to CDC through NORS. Current and historical forms are available on the Reporting Forms page.
Strength-of-Evidence Classification
A multidisciplinary panel from CDC and EPA reviews and classifies waterborne disease outbreak reports according to the strength of epidemiologic, clinical laboratory, and environmental evidence implicating water (see table below). These classifications started with the publication of the 1989-1990 surveillance report 1. Outbreak reports with limited or no environmental data might be included in WBDOSS. Outbreak reports that lack epidemiologic data linking the outbreak to water do not appear in published summaries.
When interpreting the strength-of-evidence classification (class) assigned to an outbreak, it is important to note that outbreaks and their investigations occur under different circumstances and that not all outbreaks can be investigated rigorously. Outbreak class does not necessarily indicate the adequacy and completeness of the investigation. Multiple factors, such as how quickly an outbreak is detected, affect the ability to collect optimal epidemiologic, clinical laboratory, and environmental data.
Strength-of-Evidence Classification of Investigations of Waterborne Disease Outbreaks — United States
| Class | Epidemiologic and clinical laboratory data | Environmental data |
| I | Provided and adequate | Provided and adequate |
| Epidemiologic data provided about exposed and unexposed people, with relative risk or odds ratio ≥2 or p-value ≤0.05; OR Molecular characterization of pathogens linked multiple people who had a single identical exposure |
Laboratory data or historic information (for example, history of a chlorinator or acid feed pump malfunction, no detectable free-chlorine residual, or a breakdown in circulation system); OR Molecular characteristics of pathogens isolated from water and at least one clinical specimen were identical |
|
| II | Provided and adequate | Not provided or inadequate |
| Epidemiologic data provided about exposed and unexposed persons, with relative risk or odds ratio ≥2 or p-value ≤0.05; OR Molecular characterization of pathogens linked multiple people who had a single identical exposure |
For example, laboratory testing of water not conducted and no historic information available | |
| III | Provided but limited | Provided and adequate |
| Epidemiologic data provided that did not meet the criteria for Class I or II, or claim made that ill people had no exposures in common besides water, but no data provided | Laboratory data or historic information(for example , history of a chlorinator or acid feed pump malfunction, no detectable free-chlorine residual, or a breakdown in circulation system); OR Molecular characteristics of pathogens isolated from water and at least one clinical specimen were identical |
|
| IV | Provided but limited | Not provided or inadequate |
| Epidemiologic data provided that did not meet the criteria for Class I or II, or claim made that ill people had no exposures in common besides water, but no data provided | For example, no laboratory testing of water and no historic information available |
- Herwaldt BL, Craun GF, Stokes SL, Juranek DD. Waterborne-disease outbreaks, 1989–1990.[PDF – 22 pages] MMWR Morb Mortal Wkly Rep. 1991;40(SS-3):1-21.