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Outbreaks Associated With Environmental and Undetermined Water Exposures — United States, 2011–2012

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Outbreaks Associated With Environmental and Undetermined Water Exposures — United States, 2011–2012

MMWR Weekly
Vol. 64, No. 31
August 14, 2015
PDF of this issue

Outbreaks Associated With Environmental and Undetermined Water Exposures — United States, 2011–2012


August 14, 2015 / 64(31);849-851

Karlyn D. Beer, PhD1,2*; Julia W. Gargano, PhD2*; Virginia A. Roberts, MSPH2Hannah E. Reses2Vincent R. Hill, PhD2Laurel E. Garrison, MPH3Preeta K. Kutty, MD3Elizabeth D. Hilborn, DVM4Timothy J. Wade, PhD4Kathleen E. Fullerton, MPH2Jonathan S. Yoder, MPH, MSW2
Exposures to contaminated water can lead to waterborne disease outbreaks associated with various sources, including many that are classified and reported separately as drinking water (1) or recreational water§ (2). Waterborne disease outbreaks can also involve a variety of other exposures (e.g., consuming water directly from backcountry or wilderness streams, or inhaling aerosols from cooling towers and ornamental fountains). Additionally, outbreaks might be epidemiologically linked to multiple water sources or may not have a specific water source implicated.
This report describes waterborne disease outbreaks associated with environmental and undetermined water exposures (combining and replacing the previously reported categories "water not intended for drinking," "water of unknown intent," and "other nonrecreational water") (3,4), in which the first illness occurred in 2011 or 2012. Outbreaks that were reported to the Waterborne Disease and Outbreak Surveillance System ( through the electronic National Outbreak Reporting System ( as of October 30, 2014, were included. Data collected for each outbreak include the numbers of cases of illness, hospitalizations, and deaths; the suspected or confirmed etiologic agent; the implicated water source; and the setting of exposure.
During 2011–2012, public health officials from 11 states reported 18 outbreaks associated with environmental or undetermined water exposures, causing 280 cases of illness, 67 hospitalizations (24% of cases), and 10 deaths (Table). These 18 outbreaks included 15 legionellosis outbreaks that resulted in 254 cases and all 10 deaths. The legionellosis outbreaks occurred in hotels and motels (n = four), hospitals and healthcare facilities (n = three),** long-term–care facilities (n = three), an indoor workplace/office (n = one), a factory/industrial setting (n = one), a mobile home park (n = one), a resort (n = one), and a multi-use facility (n = one). Five legionellosis outbreaks had a known water source, including ornamental fountains (n = three), a cooling tower (n = one), and a storage tank (n = one). For 10 legionellosis outbreaks the water source was undetermined. Among these, one outbreak had multiple implicated sources (drinking water, spa, and cooling system), and the remaining nine had insufficient data to implicate a particular source. Five of the 10 deaths caused by Legionella were health care facility–associated, including two associated with long-term care facilities, two with hospitals, and one with an unknown type of health care facility. In addition to the 15 legionellosis outbreaks, three Giardia intestinalis outbreaks occurred, following drinking of untreated water directly from rivers or streams in outdoor settings.
Waterborne disease outbreaks not associated with drinking water or recreational water have been increasingly reported during the past 10 years. The increase is primarily associated with an increasing number of reported Legionella outbreaks, concomitant with the rise in Legionella outbreaks associated with drinking water systems (1) ( The variety of settings and water sources implicated in theLegionella outbreaks reported here highlights the complexity of Legionella control and mitigation in the built environment, particularly in settings where susceptible persons congregate, such as hospitals, long-term care facilities, and other healthcare settings (5). Outbreaks associated with untreated water sources highlight the importance of properly treating water for drinking in backcountry settings ( Continued support for enhanced epidemiologic and environmental investigations of waterborne disease outbreaks would enable better classification of outbreaks with undetermined water exposures. Subsequently, closer examination of the reported outbreaks with emerging environmental and undetermined water exposures might reveal opportunities for detecting and preventing disease associated with the diverse water exposures encountered in everyday life.
1Epidemic Intelligence Service, CDC; 2Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, CDC; 3Division of Bacterial Diseases, National Center for Immunization and Respiratory Diseases, CDC; 4Environmental Protection Agency.
Corresponding author: Karlyn Beer,, 404-718-1151.


  1. Beer KD, Gargano JW, Roberts VA, et al. Surveillance for waterborne disease outbreaks associated with drinking water—United States, 2011–2012. MMWR Morb Mortal Wkly Rep 2015;64:842–8.
  2. Hlavsa MC, Roberts VA, Kahler AM, et al. Outbreaks of illness associated with recreational water—United States, 2011–2012. MMWR Morb Mortal Wkly Rep 2015;64:668–72.
  3. Brunkard JM, Ailes E, Roberts VA, et al. Surveillance for waterborne disease outbreaks associated with drinking water—United States, 2007–2008. MMWR Surveill Summ 2011;60(No. SS-12):38–68.
  4. CDC. Surveillance for waterborne disease outbreaks associated with drinking water and other nonrecreational water—United States, 2009–2010. MMWR Morb Mortal Wkly Rep 2013;62:714–20.
  5. Fields BS, Benson RF, Besser RE. Legionella and Legionnaires' disease: 25 years of investigation. Clin Microbiol Rev 2002;15:506–26.

* These authors contributed equally to this work.
Drinking water, also called potable water, is water for human consumption (e.g., drinking, bathing, showering, hand washing, teeth brushing, food preparation, dishwashing, maintaining oral hygiene) and includes water collected, treated, stored, or distributed in public and individual water systems, as well as bottled water.
§ Recreational water includes water in venues that are treated (e.g., pools, hot tubs, spas) or untreated (e.g., lakes, oceans).
One previously unreported outbreak with first case onset date in 2010 is reported in the Table, but not summarized in text.
** Characteristics of hospitals and health care facilities (e.g., inpatient vs. outpatient) are not systematically collected in the National Outbreak Reporting System (NORS); however, long-term care facility settings are specified in NORS and might be reported as a subset of hospitals and health care facilities. Of three health care–associated legionellosis outbreaks, two were reported to have occurred in hospitals with inpatient facilities; the third occurred in an unspecified type of health care facility.

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