Outbreaks of illness associated with recreational water use result from exposure to chemicals or infectious pathogens in recreational water venues that are treated (eg, pools and hot tubs or spas) or untreated (eg, lakes and oceans). For 2011–2012, the most recent years for which finalized data were available, public health officials from 32 states and Puerto Rico reported 90 recreational water–associated outbreaks to CDC's Waterborne Disease and Outbreak Surveillance System (WBDOSS) via the National Outbreak Reporting System (NORS). The 90 outbreaks resulted in at least 1,788 cases, 95 hospitalizations, and one death. Among 69 (77%) outbreaks associated with treated recreational water, 36 (52%) were caused by Cryptosporidium. Among 21 (23%) outbreaks associated with untreated recreational water, seven (33%) were caused by Escherichia coli (E. coli O157: H7 or E. coli O111). Guidance, such as the Model Aquatic Health Code (MAHC), for preventing and controlling recreational water–associated outbreaks can be optimized when informed by national outbreak and laboratory (eg, molecular typing of Cryptosporidium) data.

A recreational water–associated outbreak is the occurrence of similar illnesses in two or more persons, epidemiologically linked by location and time of exposure to recreational water or recreational water–associated chemicals volatilized into the air surrounding the water. Public health officials in the 50 states, the District of Columbia, US territories, and Freely Associated States* voluntarily report outbreaks of recreational water–associated illness to CDC. In 2010, waterborne outbreaks became nationally notifiable. This report summarizes data on recreational water–associated outbreaks electronically reported by October 30, 2014 to CDC's WBDOSS (http://www. cdc. gov/healthywater/surveillance/) for 2011 and 2012 via NORS.† Data requested for each outbreak include the number of cases, § hospitalizations, and deaths; etiology; setting (eg, hotel) and venue (eg, hot tub or spa) where the exposure occurred; earliest illness onset date; and illness type. All outbreaks are classified according to the strength of data implicating recreational water as the outbreak vehicle (1).¶ Outbreak reports classified as Class I have the strongest supporting epidemiologic, clinical laboratory and environmental health data, and those classified as Class IV, the weakest. Classification does not assess adequacy or completeness of investigations.** Negative binomial regression (PROC GENMOD in SAS 9.3 [Cary, NC]) was used to assess trends in the number of outbreaks over time.