Outbreaks of Illness Associated With Recreational Water — United States, 2011–2012

Michele C. Hlavsa, MPH; Virginia A. Roberts, MSPH; Amy M. Kahler, MS; Elizabeth D. Hilborn, DVM; Taryn R. Mecher, MPH; Michael J. Beach, PhD; Timothy J. Wade, PhD; Jonathan S. Yoder, MPH

Disclosures

Morbidity and Mortality Weekly Report. 2015;64(24):668-672. 

In This Article

Introduction

Outbreaks of illness associated with recreational water use result from exposure to chemicals or infectious pathogens in recreational water venues that are treated (e.g., pools and hot tubs or spas) or untreated (e.g., 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 (e.g., 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, U.S. 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 (e.g., hotel) and venue (e.g., 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.

For the years 2011 and 2012, public health officials from 32 states and Puerto Rico reported 90 recreational water–associated outbreaks (http://www.cdc.gov/healthywater/surveillance/rec-water-tables-figures.html) (Figure 1), which resulted in at least 1,788 cases, 95 (5%) hospitalizations, and one death. Etiology was confirmed for 73 (81%) outbreaks: 69 (77%) outbreaks were caused by infectious pathogens, including two outbreaks with multiple etiologies, and four (4%) by chemicals ( Table ). Among the outbreaks caused by infectious pathogens, 37 (54%) were caused by Cryptosporidium. On the basis of data reported to CDC, 37 (41%) of the 90 outbreak reports were categorized as class IV.

Figure 1.

Number* of outbreaks associated with recreational water, by month — United States, 2011–2012
* Total n = 90.
Numbers for 2011 and 2012 are combined for each month.

Outbreaks associated with treated recreational water accounted for 69 (77%) of the 90 outbreaks reported for 2011–2012, and resulted in at least 1,309 cases, 73 hospitalizations, and one reported death. The median number of cases reported for these outbreaks was seven (range: 2–144 cases). Hotels (e.g., hotel, motel, lodge, or inn) were the setting of 13 (19%) of the treated recreational water–associated outbreaks. Twelve (92%) of these 13 outbreaks started outside of June–August; ten (77%) were at least in part associated with a spa. Among the 69 outbreaks, 36 (52%) were caused by Cryptosporidium. The 69 outbreaks had a seasonal distribution, with 42 (61%) starting in June–August (Figure 1). Acute gastrointestinal illness was the disease manifestation in 34 (81%) of these summer outbreaks, with Cryptosporidium causing 32 (94%) of them. Since 1988, the year that the first U.S. treated recreational water–associated outbreak of cryptosporidiosis was detected[2,3] (Figure 2), the number of these outbreaks reported annually (range: 0–40 outbreaks) has significantly increased (negative binomial regression; p<0.001). Incidence of these cryptosporidiosis outbreaks has also, at least in part, driven the significant increase (negative binomial regression; p<0.001) in the overall number of recreational water–associated outbreaks reported annually (range: 6–84).

Figure 2.

Number* of outbreaks associated with recreational water, by year — United States, 1978–2012
* Total n = 879.

For 2011–2012, 21 (23%) outbreaks were associated with untreated recreational water. These outbreaks resulted in at least 479 cases and 22 hospitalizations. The median number of cases reported for these outbreaks was 16 (range: 2–125). Twenty (95%) of these outbreaks were associated with fresh water; 18 (86%) began in June–August; and seven (33%) were caused by E. coli O157:H7 or O111. One outbreak associated with exposure to cyanobacterial toxins was reported.

*Includes Marshall Islands, Federated States of Micronesia, and Republic of Palau.
Forms and guidance available at http://www.cdc.gov/nors/forms.html; outbreaks resulting from recreational water exposures on cruise ships are not reported to WBDOSS.
§If based on the estimated number of total cases, reporting agencies were not asked to provide supporting evidence.
Classes delineated at http://www.cdc.gov/healthywater/surveillance/recreational/outbreak-classifications.html.
**Outbreaks and subsequent investigations occur under different circumstances, and not all outbreaks can be vigorously investigated. Multiple factors contribute to the ability to collect and report optimal epidemiologic, clinical laboratory, and environmental health data.

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