Outbreaks Associated with Treated Recreational Water — United States, 2000–2014

Outbreaksassociated with exposure to treated recreational water can be causedby pathogens or chemicals in venues such as pools, hot tubs/spas, and interactive water play venues (i.e., water playgrounds). During 2000-2014, public health officials from 46 states and Puerto Rico reported 493 outbreaksassociated with treated recreational water. These outbreaksresulted in at least 27,219 cases and eight deaths. Among the 363 outbreakswith a confirmed infectious etiology, 212 (58%) were causedby Cryptosporidium(which causespredominantly gastrointestinal illness), 57 (16%) by Legionella(which causes Legionnaires' disease, a severe pneumonia, and Pontiac fever, a milder illness with flu-like symptoms), and 47 (13%) by Pseudomonas (which causes folliculitis["hot tub rash"] and otitis externa ["swimmers' ear"]). Investigations of the 363 outbreaksidentified 24,453 cases; 21,766 (89%) were causedby Cryptosporidium, 920 (4%) by Pseudomonas, and 624 (3%) by Legionella. At least six of the eight reported deaths occurred in persons affected by outbreaks causedby Legionella. Hotels were the leading setting, associated with 157 (32%) of the 493 outbreaks. Overall, the outbreakshad a bimodal temporal distribution: 275 (56%) outbreaksstarted during June-August and 46 (9%) in March. Assessment of trends in the annual counts of outbreaks causedby Cryptosporidium, Legionella, or Pseudomonas indicate mixed progress in preventing transmission. Pathogens able to evade chlorine inactivation have become leading outbreaketiologies. The consequent outbreakand case counts and mortality underscore the utility of CDC's Model Aquatic Health Code (https://www.cdc.gov/mahc) to prevent outbreaksassociated with treated recreational water.