The U.S. Centers for Disease Control reports in Morbidity and Mortality Weekly that advances in water management and sanitation have substantially reduced waterborne disease in the United States, although outbreaks continue to occur (1). Public health agencies in the U.S. states and territories* report information on waterborne disease outbreaks to the CDC Waterborne Disease and Outbreak Surveillance System (http://www.cdc.gov/healthywater/surveillance/index.html).

For 2011–2012, 32 drinking water–associated outbreaks were reported, accounting for at least 431 cases of illness, 102 hospitalizations, and 14 deaths. Legionella was responsible for 66% of outbreaks and 26% of illnesses, and viruses and non-Legionella bacteria together accounted for 16% of outbreaks and 53% of illnesses. The two most commonly identified deficiencies† leading to drinking water–associated outbreaks were Legionella in building plumbing§ systems (66%) and untreated groundwater (13%). Continued vigilance by public health, regulatory, and industry professionals to identify and correct deficiencies associated with building plumbing systems and groundwater systems could prevent most reported outbreaks and illnesses associated with drinking water systems.

This report provides information on drinking water–associated¶ waterborne disease outbreaks in which the first illness occurred in 2011 or 2012** (http://www.cdc.gov/healthywater/surveillance/drinking-surveillance-reports.html), and summarizes outbreaks reported to the Waterborne Disease and Outbreak Surveillance System through the electronic National Outbreak Reporting System (http://www.cdc.gov/nors/about.html) as of October 30, 2014. For an event to be defined as a waterborne disease outbreak, two or more persons must be linked epidemiologically by time, location of water exposure, and case illness characteristics; and the epidemiologic evidence must implicate water as the probable source of illness. Data submitted for each outbreak include 1) the number of cases, hospitalizations, and deaths; 2) the etiologic agent (confirmed or suspected); 3) the implicated water system; 4) contributing factors in the outbreak; and 5) the setting of exposure.

Karlyn D. Beer, PhD1,2; Julia W. Gargano, PhD2; Virginia A. Roberts, MSPH2; Vincent R. Hill, PhD2; Laurel E. Garrison, MPH3; Preeta K. Kutty, MD3; Elizabeth D. Hilborn, DVM4; Timothy J. Wade, PhD4; Kathleen E. Fullerton, MPH2; Jonathan S. Yoder, MPH, MSW2