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Fecal Incident and Outbreak Response

The germs that cause recreational water illnesses (RWIs) can be spread when swallowing water that has been contaminated with fecal matter (poop). How? If someone has diarrhea, that person can easily contaminate an entire aquatic venue. The water is shared by all swimmers. It’s communal bathing water. It’s not sterile. It’s not drinking water.

The good news is that most germs causing RWIs are killed by chlorine within a few minutes. However, chlorine doesn’t kill everything right away. It takes time to kill germs and some germs, such as Cryptosporidium (or Crypto for short), can live in properly treated water for days. This means even the best maintained aquatic venues can spread germs.

Time to Kill or Inactivate Germs in Chlorinated Water *

Germ Time
E. coli O157:H7 Bacterium Less than 1 minute
Hepatitis A Virus About 16 minutes
Giardia Parasite About 45 minutes
Crypto Parasite About 15,300 minutes or 10.6 days 1

Should all fecal incidents be treated the same?

No. A diarrheal incident is a higher-risk event than a formed fecal incident. With most diarrheal illnesses, the number of germs found in each bowel movement decreases as the diarrhea stops and the person’s bowel movements return to normal. Therefore, a formed fecal incident is probably less of a risk than a diarrheal incident that you might not see.

Formed fecal matter might contain no germs, a few, or many which can cause illness. You won’t know. The germs that might be present are less likely to be released into the water because they are mostly contained within the formed fecal matter. However, formed fecal matter also protects germs inside from being exposed to the chlorine in the water, so prompt removal is necessary.

Should you treat a formed fecal incident as if it contains Crypto?

No. In 1999, aquatic staff volunteers from across the country collected almost 300 samples from formed fecal incidents that occurred at aquatic venues 1.

CDC then tested these samples for Crypto and Giardia. None of the sampled feces tested positive for Crypto, but Giardia was found in 4.4% of the samples collected. These results suggest that formed fecal incidents pose only a very small Crypto risk but should be treated as a risk for spreading other germs (such as Giardia). Remember, a diarrheal incident is considered to be a higher-risk event than a formed fecal incident.

  1. CDC. Prevalence of parasites in fecal material from chlorinated swimming pools — United States, 1999. MMWR Morb Mortal Wkly Rep. 2001;50(20):410–2.

Water Contamination Response Log

Aquatic staff should document each fecal incident in an aquatic venue by recording date and time of the event, whether it involved formed fecal matter or diarrhea, and the free chlorine concentration and pH at the time or observation of the event. Download a template log by clicking on the links below:


  1. Shields JM, Hill VR, Arrowood MJ, Beach MJ. Inactivation of Cryptosporidium parvum under chlorinated recreational water conditions. J Water Health 2008;6(4):513–20.

* 1 part per million (ppm) free chlorine at pH 7.5 or less and a temperature of 77°F (25°C) or higher.