Accidents in swimming pools can be serious or fatal (drowning, broken necks) but fortunately they are rare. For pool operators one of the more likely nightmares of daily operation is when someone has “a fecal accident.” In other words, someone craps in the swimming pool. CDC has guidelines for chlorinated pools (which covers most public pools; they are guidelines because regulations are on the state, not federal, level). And they just revised them. It makes interesting reading, although I suppose this is an acquired taste. Here are the details, followed by a classic dramatic re-enactment on video.
In CDC’s world, fecal accidents come in two kinds (no, not designated number one and number two!). You have your “formed stool” accidents and your “diarrheal” accidents. Still with me? Good. The formed stool variety are not as bad. First, they are less likely to have pathogens and most of the bugs of all kinds are inside the formed stool, not on the surface. Second, intestinal pathogens can cause diarrhea and diarrheal discharge is much more likely to have pathogens in it. But pools are disinfected with chlorine, so the pathogens are killed, right? Pretty much. But different pathogens are more or less sensitive to disinfection by free chlorine. Inactivation of pathogens by chlorine depends on two factors: (i) the level, measured in chlorine concentrations in parts per million [ppm]; and the length of time the pathogen is exposed to that concentration. Usually the acidity or pH of the pool water affects this time/concentration combination, expressed as contact time (CT), the product of time in minutes and concentration in ppm. Required CT times for various pathogens are determined experimentally. E. coli is killed in about a minute at the recommended chlorine levels (1 part per million [ppm] at pH 7.5) but hepatitis A virus takes about 16 minutes. Some intestinal parasites like Giardia and Cryptosporidium have resistant forms that take much longer at the levels of chlorine found in pools: 45 minutes for Giardia and 15,300 minutes (almost 11 days) for Crypto (these numbers are for 99.9% or “three nines” inactivation). It is this last number, the three nines CT for Crypto, that prompted the revision. Experiments with a pathogenic isolate convinced CDC that the previous CT of 9600 was inadequate and needed to be bumped up to 15,300 (note that at 1 ppm a CT of 15,300 translates to 15,300 minutes of chlorine contact). So for Giardia and Crypto we are talking really long disinfectant times at 1 ppm. If you want to make sure the pool is safe from these guys you have to close the pool and ramp up the chlorine levels.
Close for how long? Ramp up how high? That’s where the formed stool and diarrheal distinction comes in. In 1999 CDC asked selected pool staff from around the country to collect (using a net) formed stool samples from some 300 fecal accidents from pools and waterparks in all parts of the US. They found Giardia in 4.4% but Crypto in none of them. So a formed stool accident is unlikely to exposed other bathers to Crypto. Diarrheal discharges may have Crypto in them, however, so CDC recommends much more stringent disinfection guidelines. In either case the pool operator should try to remove the offending material (trying not to break it into pieces in the case of formed stool) after first making everyone leave the pool and any pool connected to it and using the same filter. For a formed stool accident, the chlorine is raised to 2 ppm (pH 7.2 – 7.5) and kept there for a half hour. Unfortunately the problem for a diarrheal accident is much tougher. The chlorine should be jacked up to 20 ppm and kept there for 8 hours. That’s a “come back tomorrow folks” situation. Since this is a very high chlorine level and some test kits can’t handle it, lower levels may be used but must be continued for longer. The required times are easy to calculate from the CT numbers. In either case a record should be kept in a fecal accident log.
Fecal accidents in pools have received their share of attention from Hollywood. Here is a dramatization from the cinema classic, Caddyshack. Enjoy: