Memorial Day weekend is the unofficial start of summer, and what better way to celebrate than jumping in the pool to swim a few laps?
But if you’re heading to the neighborhood pool this summer, you’ve got something new to worry about: “crypto.”
No, people aren’t dropping bitcoin in swimming pools—they’re depositing heavier loads.
Crypto (whose scientific name is Cryptosporidium) is a parasitic infection which spreads when people swallow something that has come into contact with the feces of a sick person (such as pool water). The parasite is the most common cause of diarrhea linked to swimming pools and water parks.
The Centers for Disease Control and Prevention (CDC) report that crypto can make “healthy people sick for up to three weeks with watery diarrhea, stomach cramps, nausea or vomiting, and can lead to dehydration.”
Disturbingly, the amount of U.S. crypto outbreaks has doubled in recent years, from 16 in 2014 to 32 in 2016. Individual states have also seen increased cases—Arizona identified 352 people with crypto during summer 2016, compared with no more than 62 cases in each of the five previous years.
It gets worse: while chlorine and other pool disinfectants kill most germs within minutes, crypto is a more hardy parasite. As such, the CDC recommends closing pools after contamination to “hyperchlorinate” them. The same procedure applies to “formed or diarrheal fecal incidents in small-volume venues” like hot tubs.
Swimmers themselves can also prevent the spread of crypto by not going into the pool when they have diarrhea. That sounds easy enough, but a recent survey by the Water Quality and Health Council found that 1 in 4 adults swim within one hour of having diarrhea, and 3 in 5 adults admit to swallowing pool water (which is likely to have fecal germs in it).
Pro tip: if you drop brown stuff in the pool, all your fellow swimmers will end up blue.