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This week's CDC Morbidity and Mortality report reveals a revolting truth about swimming pools — more than half of the locations tested in 2012 showed traces of Escherichia coli, indicating that "swimmers introduced fecal material into pool water."
Also, there's an "extremely chlorine-tolerant parasite"called Cryptosporidium that you really don't want to ingest. It only takes one "incident" to cause a pool full of potential infection, according to the CDC:
A single diarrheal contamination incident can introduce 10^7–10^8 Cryptosporidium oocysts into the water, a quantity sufficient to cause infection if a mouthful of water from a typical pool is ingested.
Warning: The story only gets grosser from here. I'm sorry.
Additionally, each person has an average of 0.14 grams of fecal material on their perianal surface that could rinse into the water if swimmers fail to take a pre-swim shower with soap.
The CDC says the increased incidence of "acute gastrointestinal illness outbreaks" associated with pools underscore the need for "improved swimmer hygiene."
The findings are subject to a number of limitations, the study acknowledges, however outbreaks of illness across the country suggest a widespread concern.
The pools sampled in this study are a convenience sample of pools in metro-Atlanta, and thus study findings cannot be generalized to pools in metro-Atlanta or beyond. However, the incidence of RWI outbreaks of acute gastrointestinal illness throughout the United States suggests that swimmers frequently introduce fecal material and pathogens into recreational water throughout the country.
This study also found that:
...that the proportion of samples positive for E. coli significantly differed between membership/club and municipal pools. This finding might reflect differences in the number of swimmers who are either diapered children or children learning toileting skills.
While it's unpleasant to consider that the action plan listed below is even necessary, it's reassuring to know that one exists (no it isn't):