The best way to avoid Crypto at the pool is to keep it out of the water: stay out of the pool while you have diarrhea and for 2 weeks after it stops, shower before swimming, take children on hourly bathroom breaks and try not to swallow pool water. Crypto (short for Cryptosporidium) is a parasite that can survive in properly chlorinated pool water for days, so chlorine alone does not stop it quickly.
What is Crypto?
Crypto is a microscopic parasite that causes a diarrheal illness called cryptosporidiosis. It spreads through the stool of an infected person or animal, so one sick swimmer can contaminate a pool that many people share.
Crypto outbreaks are becoming more common. CDC’s report on cryptosporidiosis outbreaks from 2009 to 2017 (published 2019) counted 444 outbreaks and 7,465 cases, with outbreaks rising an average of about 13% a year. Pools, hot tubs, water playgrounds and other treated recreational water accounted for 156 of those outbreaks (35%) and 4,232 of the cases (57%).
Crypto is also the leading cause of outbreaks linked to pools. Of the 208 treated recreational water outbreaks CDC reviewed for 2015 to 2019 (published 2021), 76 were caused by Crypto, and those outbreaks made up 2,492 of the 2,953 cases with a confirmed cause (84%). Nearly all of these outbreaks (96%) were linked to public pools, hot tubs or water playgrounds rather than backyard pools.
How does Crypto spread in swimming pools?
Crypto spreads when someone who is sick with diarrhea gets in the water and other swimmers swallow a small amount of that water. CDC’s healthy swimming guidelines note that one diarrheal incident can release millions of germs and that even a small amount of contaminated water can make you sick.
Swallowing pool water is common. In a 2017 survey for the Water Quality and Health Council, 3 in 5 adults admitted swallowing pool water while swimming, and 1 in 4 said they would swim within an hour of having diarrhea.
Doesn’t chlorine kill Crypto?
Chlorine kills most germs spread through stool within minutes, but Crypto is far more tolerant. CDC’s guide on what to do when there is poop in the pool lists these times in properly chlorinated water:
- E. coli O157:H7: less than 1 minute
- Hepatitis A virus: about 16 minutes
- Giardia: about 45 minutes
- Crypto: about 10.6 days
CDC’s 2019 outbreak report adds that Crypto can survive more than 7 days at its recommended free chlorine level of at least 1 ppm. That is why pool safety for Crypto depends on keeping it out of the water and on extra treatment steps at public pools, covered in the operator section below.
What do parents and caregivers get wrong about Crypto?
Many caregivers do not know how Crypto spreads or how long a sick child should stay out of the pool. A Nielsen survey of 1,048 caregivers of children ages 1 to 12, fielded in July 2014 and released in May 2015 (sponsored by Lupin Pharmaceuticals, with CDC on its advisory board), found:
- Half had heard of Crypto or Giardia.
- Four in 10 believed hand sanitizers kill these parasites, which is not true.
- More than a third did not know how children catch them.
- 85% knew children with diarrhea should not swim, but 74% were unclear on how long to keep them out of the water.
Does hand sanitizer kill Crypto?
No. CDC’s 2019 Crypto outbreak report says alcohol-based hand sanitizers do not effectively kill Crypto. Washing hands with soap and water after using the toilet, after changing diapers and before eating is the better choice, at the pool and at home.
Do swim diapers keep Crypto out of the pool?
No. CDC’s tips for using swim diapers (reviewed 2024) say swim diapers and swim pants do not keep germs like Crypto in diarrhea from contaminating the water. They can only delay leaks for a few minutes. Children with diarrhea should not swim, even in a swim diaper. For children without diarrhea, check swim diapers about every 60 minutes and change them in a diaper-changing area away from the poolside.
How long should you stay out of the pool after diarrhea?
Stay out of the water for as long as you have diarrhea. If Crypto is the cause, CDC’s 2019 report recommends staying out of the water for 2 more weeks after symptoms stop, even if you feel better. The same rule applies to children, which is the guideline most caregivers in the 2014 survey were unsure about.
How can swimmers and parents prevent Crypto?
These steps from CDC’s healthy swimming guidance do the most to keep Crypto out of the water:
- Stay out of the water while sick with diarrhea, and for 2 weeks after it stops if Crypto is the cause.
- Shower for at least 1 minute before getting in.
- Take children on bathroom breaks and check diapers every hour.
- Try not to swallow pool water.
- Wash hands with soap and water; hand sanitizer is not enough for Crypto.
- Tell pool staff right away about a fecal incident.
For more pool health habits, see how to practice safe and healthy swimming and what happens when urine mixes with pool chlorine.
What can pool operators do to protect swimmers from Crypto?
Pool operators follow their local health code for fecal incidents, which for diarrhea usually means closing the pool and raising free chlorine very high for hours, as CDC’s fecal incident guide describes. Prevention matters as much: clear signs, enforced pre-swim showers, hourly bathroom breaks for young children and diaper-changing areas away from the water.
Many facilities also add a supplemental treatment step that inactivates Crypto as water passes through the equipment room. CDC’s chloramine guidance for pool operators notes that UV and ozone systems kill Crypto. Clear Comfort’s hydroxyl-based AOP was tested in a 2014 University of Colorado Boulder lab study: in a 4-liter reactor with dechlorinated tap water, it reached up to 99.99% (4-log) inactivation of Crypto by the 60-minute sample. Results in a working pool depend on flow, turnover and bather load. Clear Comfort is a supplemental system, so pools still keep a low chlorine residual.
Facility operators comparing options can read UV vs AOP for commercial pools and why commercial pools fail inspections or get shut down.
Frequently asked questions
Can you get Crypto from a chlorinated pool?
Yes. Crypto can survive in properly chlorinated pool water for days, about 10.6 days in CDC’s figures, so a pool can look clean and still spread it. Most Crypto outbreaks linked to treated water happen at public pools, hot tubs and water playgrounds.
How long should a child stay out of the pool after Crypto?
CDC recommends staying out of the water for 2 weeks after diarrhea stops, even if the child feels better. While sick, a child should not swim at all, with or without a swim diaper.
Does hand sanitizer kill Crypto?
No. CDC says alcohol-based hand sanitizers do not effectively kill Crypto. Washing hands with soap and water is the better way to remove it.
Do swim diapers stop Crypto from getting into pool water?
No. Swim diapers and swim pants can hold in solid stool for a few minutes, but CDC says they do not keep diarrhea germs like Crypto out of the water. Children with diarrhea should not swim.
How common are Crypto outbreaks in pools?
Crypto caused 76 of the 208 outbreaks linked to pools, hot tubs and water playgrounds that CDC reviewed for 2015 to 2019, more than any other germ. From 2009 to 2017, Crypto outbreaks rose an average of about 13% a year.
Run a public pool or aquatic facility? See how Clear Comfort’s supplemental AOP systems for aquatic facilities work alongside your chlorine program.
