More than 100 people in Maricopa County, Arizona, have become infected with a parasite officials believe was in at least 20 pools in the community, NBC News reported.
Cryptosporidium, or “Crypto,” causes problems from stomach cramps to vomiting to fever. Those with healthy immune systems don’t need treatment and usually recover after a week or two.
The highly contagious parasite is hard to get rid of because chlorine doesn’t always kill it, according to the Mayo Clinic.
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Officials didn’t say which pools were identified. The parasite was first discovered in Maricopa County on Aug. 4 after 19 cases were reported in July.