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

Michele C. Hlavsa, MPH; Bryanna L. Cikesh, MPH; Virginia A. Roberts, MSPH; Amy M. Kahler, MS; Marissa Vigar, MPH; Elizabeth D. Hilborn, DVM; Timothy J. Wade, PhD; Dawn M. Roellig, PhD; Jennifer L. Murphy, PhD; Lihua Xiao, DVM, PhD; Kirsten M. Yates, MPH; Jasen M. Kunz, MPH; Matthew J. Arduino, DrPH; Sujan C. Reddy, MD; Kathleen E. Fullerton, MPH; Laura A. Cooley, MD; Michael J. Beach, PhD; Vincent R. Hill, PhD; Jonathan S. Yoder, MPH

Disclosures

Morbidity and Mortality Weekly Report. 2018;67(19):547-551. 

In This Article

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.

*Includes Federated States of Micronesia, Marshall Islands, and Republic of Palau.
2013–2014 were the last years for which finalized data were available. For more information on WBDOSS, visit https://www.cdc.gov/healthywater/surveillance/index.html; outbreaks resulting from recreational water exposures on cruise ships are not reported to WBDOSS.
§Based on the estimated number of primary cases. For outbreaks that started before 2009, if both the actual and estimated case counts were reported, the estimated case count was used if the population was sampled randomly or the estimated count was calculated by applying the attack rate to a standardized population.
The two remaining deaths were in persons affected by an outbreak caused by an etiology that was unidentified but suspected to be Legionella.
**Other settings: community/municipality/public park (115 [23%] outbreaks), club/recreational facility (68 [14%]), waterpark (54 [11%]), private residence (31 [6%]), subdivision/neighborhood (21 [4%]), school/college/university (14 [3%]), unidentified (13 [3%]), camp/cabin setting (nine [2%]), child care/daycare center/day camp (six [1%]), health care facility (three [1%]), and other (two [0%]). Categories were not consistently used or defined over the study period.
††Approximately half (60 [56%]) of the 108 outbreaks with an unidentified etiology were associated with the hotel setting. Among the 60 outbreaks, 23 (38%) started during March–April; 41 (68%) were outbreaks of skin-related illness.
§§The remaining eight outbreaks were caused by norovirus (five [5%] outbreaks), Bacillus (one [1%]), nontuberculous mycobacterium (one [1%]), and Staphylococcus (one [1%]).
¶¶The 2007 number of outbreaks associated with treated recreational water and caused by Cryptosporidium (40), and thus, of outbreaks overall might be outliers. For 2007, Utah reported a statewide outbreak primarily associated with treated recreational water and caused by Cryptosporidium; neighboring states reported additional outbreaks associated with recreational water and caused by Cryptosporidium. All of these individual outbreaks might have been a single multistate outbreak. https://www.cdc.gov/mmwr/preview/mmwrhtml/ss6012a1.htm.
***Because of concerns that folliculitis might not be cultured, which means the etiology cannot be identified, a Poisson regression analysis was conducted to assess the annual number of outbreaks of skin-related illness caused by Pseudomonas or an unidentified etiology. The annual number of outbreaks decreased by 5% (95% CI = 1%–9%).

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