That crystal-clear pool water could be harboring Cryptosporidium, a parasite that can cause up to three weeks of diarrhea, stomach cramps, nausea and vomiting. Reports of widespread outbreaks of infection by the parasite, known as crypto for short, have doubled in just two years in the US, from 16 outbreaks in 2014 to 32 in 2016, and thousands of Americans are infected annually. Nearly 2,000 people were infected last year in Ohio alone. Crypto is now the most common cause of diarrhea outbreaks linked to pools and water playgrounds in the US, and it can be life-threatening for people with weakened immune systems.
This parasite usually is spread through swallowing contaminated water at swimming pools and water playgrounds. Unlike most pathogens, it can survive up to 10 days in properly chlorinated water. Advanced water-treatment systems such as those using ultraviolet light or ozone do a better job of killing crypto. Public swimming pools and water playgrounds are especially vulnerable to causing large-scale outbreaks because of the large numbers of people who use them, but crypto also can be contracted in private pools and hot tubs and in natural bodies of water.
What to do: Don’t swallow any water when you go swimming—especially when swimming in a public pool or visiting a water playground. If you do not swallow any water, you are unlikely to become infected even if crypto is present. One way to reduce the odds of ingestion is to keep your face out of the water as much as possible.
The parasite is transmitted into pool water from infected individuals via contaminated feces. To avoid being the source of contamination in a pool, don’t go swimming if you have been experiencing diarrhea, and don’t allow children to do so either. (This includes very young children in diapers—if a child has diarrhea, even the “swim diapers” designed for use in pools will not provide adequate protection for the water.) If your doctor tells you that your diarrhea is a result of crypto, do not go swimming until you have been diarrhea-free for two weeks.