Lifestyle Health Diarrhea-Causing Illness from Swimming Pools — Known as 'Crypto' — Is on the Rise, CDC Says Between 2009 and 2017, outbreaks of crypto increased by about 13 percent each year By Julie Mazziotta Julie Mazziotta Twitter Julie Mazziotta is the Sports Editor at PEOPLE, covering everything from the NFL to tennis to Simone Biles and Tom Brady. She was previously an Associate Editor for the Health vertical for six years, and prior to joining PEOPLE worked at Health Magazine. When not covering professional athletes, Julie spends her time as a (very) amateur athlete, training for marathons, long bike trips and hikes. People Editorial Guidelines Published on June 28, 2019 05:27 PM Share Tweet Pin Email If you’re headed to the pool this summer, make sure it’s one you trust before you dive in: According to the Centers for Disease Control, outbreaks are on the rise of a diarrheal illness from swimming pools. Outbreaks of the parasite cryptosporidium, known as crypto, have increased year after year, the CDC says in a new report. Crypto is “the leading cause of outbreaks of diarrhea linked to water,” the organization says. The CDC analyzed cases of crypto between 2009 and 2017, and found that there were 444 outbreaks over that span, leading to 7,465 reported cases. And during that time, the number of cases increased by an average of 13 percent each year. Most cases — 35 percent — occurred when people swallowed water in contaminated pools or water parks. Some also came up from contact with infected cattle, and others from childcare centers. The crypto parasite causes cryptosporidiosis, a watery diarrhea that can persist for up to three weeks. It largely affects children aged 1 to 4, the CDC says, and young children who are not yet toilet trained and spend time in wading pools and water parks. RELATED VIDEO: Woman Dies From Flesh-Eating Bacteria After Eating Oysters: ‘She Knew She Was Dying,’ Says Relative To limit cases of crypto, the CDC is discouraging people from going swimming or attending daycare with diarrhea, and is instructing people to wash their hands after interacting with animals. Most people will recover from crypto without a problem, the CDC says, and just need fluids to prevent dehydration — but people with weakened immune systems, as well as babies, may need more intense treatment.