Health officials are asking Americans to take precautions over reports that “crypto,” a fecal parasite that can be transmitted via swimming pools, is on the rise. The parasite’s full name is cryptosporidium. It causes cryptosporidiosis, which can leave healthy adults suffering from “profuse, watery diarrhea” for as long as three weeks. The effects can be worse for children, pregnant women and those with compromised immune systems. It only takes one person having diarrhea in the water to contaminate all of the water in a pool. Don’t swim or let your kids swim if sick with diarrhea. Though it’s almost never fatal, one death has been reported since 2009, according to the CDC. Another 287 people were hospitalized between 2009 and 2017, the CDC says.