This article is more than 5 years old. Information may no longer be current.
Chlorine, filtration may not be enough to protect against Cryptosporidium
Click Here to Manage Email Alerts
Chlorine disinfection and filtration systems may not be enough to protect water park patrons from Cryptosporidium, CDC researchers concluded in a study.
The CDC recently published a report of a outbreak at an Idaho waterpark that involved at least 50 of 154 attendees that met the clinical (n=45) or confirmed (n=5) case definition for Cryptosporidium.
On Aug. 6, 2007, Idaho’s Central District Health Department received a complaint of several ill people with watery diarrhea consistent with cryptosporidiosis after attendance at a municipal splash park on July 26.
The next day, health officials interviewed 20 people who attended a party at the splash park on July 26, and noted of those, 12 reported gastrointestinal illness that began about six days after exposure, including eight people who reported watery diarrhea. All of those who reported being sick had been exposed to the splash-feature water and six reported exposure to water from a nearby drinking fountain.
Researchers then initiated telephone interviews of municipal park visitors who attended reservation-only gatherings at an onsite pavilion. They limited the interviews to the first 154 respondents contacted, representing nine of the 12 reservation parties and noted of those, 50 were ill with Cryptosporidium.
Because those who were positive for Cryptosporidium were ill between July 23 and Aug. 10, health department officials theorized that initial contamination of splash park water by an ill visitor likely caused persistent contamination of the splash park system and resulted in ongoing transmission. They said that similar outbreaks have occurred at other splash parks that lacked ultraviolet or ozone treatment systems. The water park was only allowed to reopen after they installed an ultraviolet treatment system, improved hygiene facilities, hired attendants to monitor for nonhygienic behaviors by visitors and posted signs instructing visitors not to drink the splash-feature water.
The researchers noted several limitations to their study, including: “The total number of visitors to the splash park during the study period could not be determined. ... Second, limited staff resources might have led to selection bias by restricting interviews to those people able to be contacted most quickly, perhaps biasing the study toward people more likely to be at home and ill. Third, a statewide cryptosporidiosis outbreak involving multiple recreational water venues was occurring at the same time as the municipal splash park outbreak, and ill people might have been exposed to other contaminated sources of recreational water, potentially confounding the results.” Also, the researchers noted, despite an engineering investigation, the specific source of drinking water contamination could not be determined.
They said failed backflow prevention devices might have allowed contaminated splash park water to enter the municipal drinking water line supplying the drinking fountain; most ill people (27/40) did not use the drinking fountain.
The health officials said that the water park had been recently constructed and it was an unregulated splash park. The researchers said prior consultation with health department staff might have identified and corrected the potential backflow problems.
MMWR. 2009;58:615-618.