Rate of Cryptosporidiosis Outbreaks Linked to Pools and Water Parks Growing


Outbreaks of the water-borne pathogen increased an average of 13% each year between 2009 and 2017.

With the Fourth of July holiday rapidly approaching, the US Centers for Disease Control and Prevention (CDC) is cautioning the public to be careful before jumping into a pool or visiting a waterpark.

The summer months are the peak season for outbreaks of cryptosporidiosis, a disease that is caused by the parasite Cryptosporidium (Crypto) which causes watery diarrhea. Since the early 2000s, the parasite has been the leading cause of water-borne disease outbreaks linked to recreational water in the United States and new data indicate these outbreaks are only on the rise.

Individuals can fall ill after swallowing the Crypto parasite in contaminated water or food or after having contact with infected people or animals. The disease can feature watery diarrhea that may persist for up to 3 weeks in immunocompetent patients and lead to life-threatening malnutrition in immunocompromised individuals.

According to a recent article in the CDC’s Morbidity and Mortality Weekly Report outbreaks of Crypto increased an average of 13% each year between 2009 and 2017.

The report describes 444 outbreaks reported during the time period, which resulted in 7465 cases, 287 hospitalizations and 1 death. In total, 156 outbreaks, which accounted for 4232 cases, were found to be related to pathogen exposure in pools or waterparks. Other outbreaks were linked to contact with cattle, contact with infected individuals in child care settings, or drinking unpasteurized milk or apple cider.

“Negative binomial regression analysis indicated that during 2009—2017, the overall annual number of reported cryptosporidiosis outbreaks increased an average of 12.8% per year (95% confidence interval [CI] = 7.6%–18.0%),” the authors of the report write. “The annual number of reported treated recreational water-associated outbreaks increased an average of 14.3% (95% CI = 3.4%–25.2%) per year during 2009–2016 (p = 0.010); however, because of a decline in reported outbreaks in 2017, no trend was found for the annual number of treated recreational water-associated outbreaks during 2009–2017 (p = 0.293).”

Crypto outbreaks can be challenging as the parasite is difficult to kill because of an outer shell that allows it to survive for days in chlorinated waters and on surfaces disinfected with bleach.

Outbreaks of Crypto are defined as 2 or more cases that can be epidemiologically linked to a common source by both location and time of exposure. During the study period, 40 states and Puerto Rico reported outbreaks of the water-borne pathogens. It is required that health officials throughout the United States report outbreaks to the CDC via the National Outbreak Reporting System.

In 2010 the CDC launched CryptoNet, a DNA fingerprinting-based system for illnesses caused by the Crypto parasite. Through the system, approximately 40 Crypto species have been identified thus far, of which 17 species and 4 additional genotypes have been reported to infect humans. Given that individual species, genotypes, and subtypes can have unique qualities including host ranges it is important to conduct molecular characterization in order to learn more about outbreak exposures and sources.

According to the authors of the report, in order to quell the rise in Crypto outbreaks, it is important to disseminate information about prevention which includes discouraging swimming or attending child care while experiencing diarrhea and encouraging hand washing following contact with animals or livestock.

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