Community-Wide Recreational Water-Associated Outbreak of Cryptosporidiosis and Control Strategies--Maricopa County, Arizona, 2016.

Author:Iverson, Sally Ann


Cryptosporidiosis, caused by the parasite Cryptosporidium, has emerged as the leading cause of treated aquatic facility-associated outbreaks in the U.S. (Hlavsa et al., 2015) and was responsible for at least 32 outbreaks in 2016 (Hlavsa et al., 2017). Persons are infected when they ingest Cryptosporidium oocysts, the parasite's infectious life stage, in food or water contaminated with fecal matter, or after contact with infected persons or animals. Within 2 weeks (mean of 7 days), infected persons might experience profuse, watery diarrhea, which can last [less than or equal to] 30 days in immunocompetent persons (Heymann, 2015). Additional symptoms include abdominal cramping, anorexia, nausea, vomiting, and fever. Oocyst shedding in stool typically ceases [less than or equal to] 2 weeks after complete symptom resolution (Jokipii & Jokipii, 1986).

The two species responsible for >90% of human cryptosporidiosis occurrences are C. hominis, which is primarily maintained in a human-to-human transmission cycle, and C. parvum (Bouzid, Hunter, Chalmers, & Tyler, 2013). Among outbreak specimens subtyped since the 1990s, C. hominis IfA12G1 has been a leading etiology of recreational water-associated outbreaks of cryptosporidiosis in the U.S. (Fill et al., 2017; D. Roellig, personal communication, September 2016).

Cryptosporidium presents a unique challenge to treated aquatic venues, such as pools, waterparks, and interactive water features (splash pads) because infected persons shed the parasite in stool for an extended period of time (Jokipii & Jokipii, 1986). Cryptosporidium has a very low infectious dose, with ingestion of [less than or equal to] 10 oocysts being sufficient to cause illness (Chappell et al., 2006). Cryptosporidium is extremely chlorine tolerant and can survive in a properly chlorinated pool for [greater than or equal to] 7 days (Murphy, Arrowood, Hlavas, Beach, & Hill 2015; Shields, Hill, Arrowood, & Beach, 2008). A single fecal contamination event in a chlorine-treated aquatic venue can lead to infection in many swimmers and focal outbreaks (i.e., involving one venue) can quickly turn into community-wide outbreaks if infected persons swim in multiple venues or transmit the parasites in other settings such as child care facilities (Painter, Hlavsa, Collier, Xiao, & Yoder, 2015).

Maricopa County, Arizona, is home to >4 million persons who enjoy an extended swimming season at approximately 9,000 public-treated aquatic venues, of which >90% are outdoor venues. In early August 2016, the Maricopa County Department of Public Health was notified of a cluster of diarrheal illness (later identified as C. hominis infection) in members of a children's baseball team that swam at a large treated aquatic facility in Maricopa County (water park A) on July 22. Simultaneously, an increase in laboratory-confirmed cases of cryptosporidiosis was detected through passive surveillance. This article describes the investigation and response for this cryptosporidiosis outbreak, including strategies to control the outbreak and remediate multiple public-treated aquatic venues in the county.


An outbreak case of cryptosporidiosis was defined as onset of diarrhea, abdominal cramping, or vomiting in a resident of Maricopa County during July 1-December 7, 2016. Laboratory-confirmed cases had evidence of Cryptosporidium infection by one or more of the following stool specimen tests: direct fluorescent antibody test, polymerase chain reaction (PCR) enzyme immunoassay, light microscopy of stained specimen, and immunochromatographic (rapid card) tests. A probable case was defined as lacking laboratory confirmation but having a clinical illness and an epidemiologic link to a confirmed case. We based case detection on provider and electronic laboratory reports of confirmed cryptosporidiosis cases; we identified probable cases through interviews with persons having a confirmed case. The Centers for Disease Control and Prevention's (CDC) CryptoNet laboratory performed the genotyping (Hlavsa et al., 2017).

We used a standardized questionnaire with patients or guardians of patients

All interviewed persons were advised to avoid swimming until 2 weeks after the complete resolution of diarrhea. On September 1, 2016, an alert was sent to schools and child care centers. The alert included the following prevention and control recommendations: educate staff and parents regarding the outbreak, exclude any child with diarrhea, terminate all water play and swimming activities, practice good hand hygiene and diapering techniques, and clean and disinfect surfaces and objects to effectively remove and inactivate Cryptosporidium oocysts.

Remediation of public chlorine-treated aquatic venues such as pools, hot tubs and spas, water parks, and interactive water play facilities was targeted based on interview responses. During August 5-18, remediation of each public-treated aquatic venue was recommended when two or more persons from different households with confirmed cryptosporidiosis cases reported exposure to the same aquatic venue in the 2 weeks before symptom onset or while diarrhea was ongoing. During August 19-December 7, 2016, remediation was recommended for every public-treated aquatic venue that a person with a confirmed case reported as a source of exposure in the 2 weeks before symptom onset or while diarrhea was ongoing.

Venues were referred to Maricopa County Environmental Services Department (MCESD) and an employee from MCESD attempted to visit the venue within 24 hr of receiving the referral. Venue operators were counseled and given guidelines from CDC for hyperchlorination to inactivate Cryptosporidium (CDC, 2014). Remediation of residential pools was not recommended; residential pool owners who expressed concern that a person with cryptosporidiosis swam in their pool were advised to close the pool for 2 weeks.

On October 25, 2016, a self-administered survey was distributed to attendees of a community stakeholder meeting for facility operators to assess the response to the outbreak among public-treated aquatic facilities. This survey assessed the presence of supplementary water treatment systems, such as ultraviolet (UV) or ozone for Cryptosporidium in 2016, and any plans for installation of supplementary systems before the 2017 swimming season.


The outbreak was detected when a cluster of diarrheal illness among 35 (69%) of 51 visitors (children's baseball team and their family members) to water park A was reported; symptom onset occurred 6-7 days after visiting the water park. Additionally, interviews of 9 persons, not part of the baseball team cohort but who had positive laboratory results for Cryptosporidium, revealed 5 persons (56%) were exposed to both water park A (a large...

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