Abstact and Introduction
Introduction
Outbreaks associated with exposure to treated recreational water can be caused by 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 outbreaks associated with treated recreational water. These outbreaks resulted in at least 27,219 cases and eight deaths. Among the 363 outbreaks with a confirmed infectious etiology, 212 (58%) were caused by Cryptosporidium (which causes predominantly 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 outbreaks identified 24,453 cases; 21,766 (89%) were caused by Cryptosporidium, 920 (4%) by Pseudomonas, and 624 (3%) by Legionella. At least six of the eight reported deaths occurred in persons affected by outbreaks caused by Legionella. Hotels were the leading setting, associated with 157 (32%) of the 493 outbreaks. Overall, the outbreaks had a bimodal temporal distribution: 275 (56%) outbreaks started during June–August and 46 (9%) in March. Assessment of trends in the annual counts of outbreaks caused by Cryptosporidium, Legionella, or Pseudomonas indicate mixed progress in preventing transmission. Pathogens able to evade chlorine inactivation have become leading outbreak etiologies. The consequent outbreak and case counts and mortality underscore the utility of CDC's Model Aquatic Health Code (https://www.cdc.gov/mahc) to prevent outbreaks associated with treated recreational water.
An outbreak associated with recreational water is the occurrence of similar illnesses in two or more persons, epidemiologically linked by location and time of exposure to recreational water or to pathogens or chemicals aerosolized or volatilized from recreational water into the surrounding air. Public health officials in the 50 states, the District of Columbia, U.S. territories, and Freely Associated States* voluntarily report outbreaks associated with recreational water to CDC. This report focuses on data in two groups of outbreaks associated with treated recreational water: 1) those that started during 2000–2012 and were previously summarized[1] and 2) those that started during 2013–2014 and were electronically reported to the Waterborne Disease and Outbreak Surveillance System (WBDOSS)† by December 31, 2015 (https://www.cdc.gov/healthywater/surveillance/rec-water-tables-figures.html). Data on each outbreak included case count,§ number of deaths, etiology, setting (e.g., hotel) and venue (e.g., pool, hot tub/spa) where the exposure occurred, and earliest illness onset date. Poisson regression analysis was conducted to assess the trend in the annual counts of outbreaks, except when overdispersion required the use of negative binomial regression analysis.
During 2000–2014, public health officials from 46 states and Puerto Rico reported 493 outbreaks associated with treated recreational water, which resulted in at least 27,219 cases (Table) and eight deaths. Etiology was confirmed for 385 (78%) outbreaks. Among these, 363 (94%) were caused by pathogens (including four caused by both Cryptosporidium and Giardia) and resulted in at least 24,453 cases. Twenty-two (6%) outbreaks were caused by chemicals and resulted in at least 1,028 cases. Among the 363 outbreaks with a confirmed infectious etiology, 212 (58%) were caused by Cryptosporidium, 57 (16%) by Legionella, and 47 (13%) by Pseudomonas. Of the 24,453 cases, 21,766 (89%) were caused by Cryptosporidium, 920 (4%) by Pseudomonas, and 624 (3%) by Legionella. Of the 212 outbreaks caused by Cryptosporidium, 24 (11%) each affected >100 persons; four of these outbreaks each affected ≥2,000 persons. At least six of the eight deaths,¶ which all occurred after 2004, were in persons affected by outbreaks caused by Legionella.
Hotels** (i.e., hotels, motels, lodges, or inns) were the leading setting associated with 157 (32%) of the 493 outbreaks. Of the 157 hotel-related outbreaks, 94 (60%)†† had a confirmed infectious etiology, 40 (43%) were caused by Pseudomonas, 29 (31%) by Legionella, and 17 (18%) by Cryptosporidium.§§ Sixty-five (41%) hotel-related outbreaks were associated with hot tubs/spas, and 47 (30%) started during February–March. Among all 493 outbreaks, a bimodal temporal distribution was observed. The 275 (56%) outbreaks that started during June–August were predominantly caused by Cryptosporidium, whereas the 46 (9%) that started in March were predominantly caused by an unidentified etiology or pathogens other than Cryptosporidium (Figure 1). Negative binomial regression analysis indicated that during 2000–2007, the annual number of outbreaks caused by Cryptosporidium increased by an average of 25% (95% confidence interval [CI] = 7%–45%) per year (Figure 2). No significant trend was found after 2007.¶¶ Poisson regression analysis indicated that during 2000–2014 the annual number of outbreaks caused by Legionella increased by an average of 13% (95% CI = 6%–21%) per year, and the annual number of Pseudomonas folliculitis outbreaks (a total of 41 outbreaks during 2000–2014) decreased by an average of 22% (95% CI = 14%–29%) per year.***
Figure 1.
Number of outbreaks associated with treated recreational water (N = 493), by etiology and month — United States, 2000–2014* *Includes outbreaks with the following etiologies: Bacillus, Campylobacter, Escherichia coli, methicillin-resistant Staphylococcus aureus, nontuberculous mycobacteria, Salmonella, Shigella, Staphylococcus, Giardia, echovirus, norovirus, or excess chlorine/disinfection by-product/altered pool chemistry.
Figure 2.
Number of outbreaks associated with treated recreational water (N = 493), by etiology and year — United States, 2000–2014 *Includes outbreaks with the following etiologies: Bacillus, Campylobacter, Escherichia coli, methicillin-resistant Staphylococcus aureus, nontuberculous mycobacteria, Salmonella, Shigella, Staphylococcus, Giardia, echovirus, norovirus, or excess chlorine/disinfection by-product/altered pool chemistry.
Morbidity and Mortality Weekly Report. 2018;67(19):547-551. © 2018 Centers for Disease Control and Prevention (CDC)
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