Cryptosporidium parvum (Photograph by Michael Wunderli via Flickr | CC-BY-SA 2.0).
Many swimming pools were already winding down in Yellowstone County this week as area school districts either begin school or prepare to start next week.
That’s probably good news for public health officials who have reported an outbreak of cryptosporidiosis, which is caused by the parasite cryptosporidium.
As of Tuesday, RiverStone Health, which is the public health department for Montana’s largest county, reported 35 confirmed cases and another 36 which are likely.
Cryptosporidiosis, or “crypto” — not to be confused with blockchain currency — is a diarrhea-causing illness which is spread when a person swallows water containing germs from the fecal matter of another person or animal. Transmission is often from swimming pools, as cryptosporidium are highly resistant to chlorine, but can also be found in open water, for example, lakes and rivers.
According to the Centers for Disease Control and Prevention, crypto is found all over the United States and world.
Casey Page, Riverstone’s interim director of communications, said that there have been outbreaks of crypto recently, but none quite as large as this in 2024. Page also said that there’s not one common point of contamination, rather several are likely.
Once a person is infected, the incubation period can range from seven to 12 days, and signs include diarrhea and sometimes vomiting. Diarrhea may be intermittent, but health officials report that most recovery fully within 30 days. Usually, cryptosporidiosis doesn’t require medical intervention, except in cases where a person is immunocompromised, according to the CDC.
The CDC also reports that usually people who have been previously infected with the disease make quick antibodies, and they usually are not sickened, or show no symptoms, upon re-infection.
Though crypto is often picked up by swimming, it can be acquired through eating contaminated food or touching objects that are contaminated, including handling the fecal matter of pets or children.
Riverstone Health reports that three people in Yellowstone County have been hospitalized for short periods recently, mostly because of dehydration. While there are anti-parasitic medications, usually medication is not necessary for treatment, Page said.
The last time public health officials investigated a crypto outbreak in Yellowstone County was in late summer in 2013 when there was a total of 23 confirmed and probable cases, according to Riverstone Health.
Public health officials recommend the following ways to stay safe while swimming in public pools or bodies of water:
- Avoid swallowing water while swimming.
- Ensure that small children wear watertight swim diapers.
- Wash your hands with soap and water after swimming or playing in the sand to avoid infecting food and surfaces (alcohol-based sanitizers are not effective against Crypto).
- Shower before swimming.
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