Waterborne Disease Outbreaks Associated With Environmental and Undetermined Exposures to Water — United States, 2013–2014

R. Paul McClung, MD; David M. Roth, MSPH; Marissa Vigar, MPH; Virginia A. Roberts, MSPH; Amy M. Kahler, MS; Laura A. Cooley, MD; Elizabeth D. Hilborn, DVM; Timothy J. Wade, PhD; Kathleen E. Fullerton, MPH; Jonathan S. Yoder, MPH, MSW; Vincent R. Hill, PhD


Morbidity and Mortality Weekly Report. 2017;66(44):1222-1225. 

In This Article

Abstract and Introduction


Waterborne disease outbreaks in the United States are associated with a wide variety of water exposures and are reported annually to CDC on a voluntary basis by state and territorial health departments through the National Outbreak Reporting System (NORS). A majority of outbreaks arise from exposure to drinking water[1] or recreational water,[2] whereas others are caused by an environmental exposure to water or an undetermined exposure to water. During 2013–2014, 15 outbreaks associated with an environmental exposure to water and 12 outbreaks with an undetermined exposure to water were reported, resulting in at least 289 cases of illness, 108 hospitalizations, and 17 deaths. Legionella was responsible for 63% of the outbreaks, 94% of hospitalizations, and all deaths. Outbreaks were also caused by Cryptosporidium, Pseudomonas, and Giardia, including six outbreaks of giardiasis caused by ingestion of water from a river, stream, or spring. Water management programs can effectively prevent outbreaks caused by environmental exposure to water from human-made water systems, while proper point-of-use treatment of water can prevent outbreaks caused by ingestion of water from natural water systems.

CDC analyzed data from waterborne disease outbreaks reported to NORS associated with environmental and undetermined exposures to water during 2013–2014. Outbreaks with an environmental exposure to water are not associated with a recreational water venue or drinking water system, but rather, are linked to other water types including water from cooling towers, industrial processes, agricultural processes, occupational settings, decorative or display settings (e.g., decorative fountains), and water consumed from natural sources such as backcountry streams.[3] Outbreaks involving an undetermined exposure to water could not be definitively linked to a single type of water exposure because of association with multiple suspected or confirmed water types (e.g., both spa and drinking water systems) or because insufficient epidemiologic, laboratory, or environmental evidence was available to identify the exposure. All outbreaks with first illness onset during 2013–2014 reported by December 31, 2015 are included in this report. NORS defines a waterborne disease outbreak as the occurrence of a similar illness in two or more persons who are linked by time and location to a common water exposure. For each outbreak, data were collected regarding the number of ill persons, hospitalizations, and deaths, along with the sex, age group, symptoms, and duration of illness for persons affected by the outbreak. Results of epidemiologic and laboratory investigations are also reported, including the suspected or confirmed etiologic agent, the type of water to which patients were exposed, and the setting of the water exposure. During the analysis, predominant illness type was assigned, and water type was further categorized as a human-made or natural water system. Human-made water systems include infrastructure intended for water storage or recirculation, whereas natural water systems include raw water that might or might not be treated at the point of exposure. Waterborne disease outbreaks associated with environmental and undetermined exposures to water from prior years have been reported previously (https://www.cdc.gov/healthywater/surveillance/environmental/environ-water-surveillance-reports.html).