What is Floating in the Pool?

We interrupt this summer vacation to bring you some really revolting information. Now that you've spent the past few weeks lounging and cavorting in your neighborhood pool - and no doubt gulping down gallons of pool water - wouldn't you like to learn more about the organisms frolicking along with you in that tepid water? Of course, and that's why I have brought you this timely article culled from data provided by the Centers for Disease Control and Prevention (CDC). I do this under the guise of providing the information necessary to care for ED patients who may be stricken by pool-related illnesses, knowing full well that the motivation for reading this is rooted in morbid curiosity about the diseases to which you've actually exposed yourself.

As eloquently described by various CDC authors, swimming is essentially communal bathing. Pool water contains various body fluids, fecal matter, dirt, and debris that wash off bodies during swimming activities. Fecal matter is regularly introduced into the water when someone has a fecal accident … or when residual fecal matter on swimmers' bodies is washed into the pool. (MMWR 2001;50:410; MMWR 2000;49:SS-4.) As might be expected, the vast majority of individuals responsible for such fecal accidents are toddlers, who are too young be held responsible for the havoc wreaked by their little misadventures in potty training.

While the number of waterborne-disease outbreaks associated with drinking water has declined dramatically over the past two decades, outbreaks related to recreational water have actually increased over the past decade (MMWR 2000; 49: SS-4). In 1998, the last year for which reporting is complete, there were 25 outbreaks of recreational water-related illnesses, of which 15 occurred in pools and hot tubs. There were 15 outbreaks of gastroenteritis, with smaller outbreaks of meningoencephalitis and dermatitis.

While a dozen or so outbreaks of gastroenteritis may not seem like a lot, consider that each outbreak often affects hundreds of people. About 1600 people contracted recreational water-related gastroenteritis in 1998. We also know that the number of reported cases greatly underestimates the total number of people who actually contracted illness - at least by order of magnitude - either because most individuals ride out the illness without seeing a doctor or because doctors fails to send stool cultures.

Parasites Afloat

The organism responsible for recreational-water-related gastroenteritis varies by the type of water in which one chooses to frolic. Cryptosporidium, a ubiquitous protozoal parasite, is the culprit in 80 percent of diarrheal outbreaks traced to pools. In a July 2000 Cryptosporidium outbreak at an Ohio pool, diarrheal illness was confirmed in 700 individuals over a two-month period (MMWR 2001;50:406). The mean age of the ill individuals was 6 years and the mean duration of illness seven days.

In addition to diarrhea, most individuals had anorexia and cramps, and half had vomiting. The authors of the report note that at least five fecal accidents, one of which was diarrheal, were observed at the pool during the epidemic, a statistic that is more nauseating than surprising. It makes one's head spin to ponder how many fecal accidents go unobserved (especially those of us with toddlers).

Disturbingly, Cryptosporidium oocytes are highly resistant to chlorine and are small enough to avoid removal by conventional pool filters. The organism may be detected - and be infectious - for several days, even in pool water containing the recommended concentration of chlorine (Emerg Infect Dis 1999;5:1). Cryptosporidium-infected individuals release very high titers of the parasite in their stool, and ingestion of as few as 10 to 100 organisms is enough to cause the disease in healthy individuals (MMWR 2000; 49: SS-4). Activities that increase the risk of getting pool water in the mouth, such as standing under a sprinkler, strongly increase the risk of illness.

Other gastrointestinal infections traced to pool exposure are E. coli O157:H7 and Shigella sonnei, each responsible for 10 percent of pool-related diarrheal outbreaks in 1998. Unlike Cryptosporidium, E. coli O157:H7, strongly associated with hemorrhagic colitis and hemolytic-uremic syndrome, is inactivated very quickly in chlorinated water (Emerg Infect Dis 1999; 5: 461). Among fresh water-related diarrheal outreaks (i.e., lakes and streams), Norwalk-like virus, E. coli O157:H7 and Cryptosporidium infections are noted, although no etiology is found for more than one-third of cases (MMWR 2000; 49:SS-4).

Other recreational waterborne illnesses have been reported with regularity. There are sporadic cases of meningoencephalitis related to Naegleria, a free-living ameba that is not generally pathogenic. In 1998, 375 triathletes contracted leptospirosis from an Illinois lake. Outbreaks of Pontiac fever (acute Legionella infection without pneumonia) and numerous cases of pseudomonas dematitis have been associated with hot tub use (MMWR 2000;49:SS-4).

Public Health Concern

With more than 400 million annual pool visits in this country, pool hygiene is a significant public health concern. Much of the burden for preventing disease rests on maintenance of appropriate standards by pool operators. It is sobering that our health lies largely in the hands of battalions of phenomenally bored teenagers. Yet even the most recent CDC guidelines express uncertainty regarding the best methods of chlorination and decontamination following accidents.

The CDC has a Healthy Swimming web site and fact sheet that advises the public not to swim when they have diarrhea, not to swallow pool water, and to wash hands after using the bathroom. It further advises parents to take kids on frequent bathroom breaks (I have to go may mean it's too late), change diapers in a restroom rather than at poolside, and to wash children before swimming. We now see the wisdom in our pool's hourly adults-only swim period, which infuriates both parents and kids but gives everyone an excuse to go to the bathroom (in the bathroom, that is) fairly frequently.

Now relax, dangle your toes in the pool, and if you really must go in the water, keep your mouth closed.