There are articles about it
here and
here. You can read about Crypto at the CDC site
here.
Interestingly, the CDC guidelines for what to do with Crypto
here says to superchlorinate for a total CT (chlorine in ppm times time in minutes) of 15,300. That's basically 10 ppm FC WITH NO CYA for 25-1/2 hours. The 40 ppm FC for 48 hours being done at the Phoenix pools would at first appear to be 7.5 times as high, but the pools in the Phoenix that were closed were probably outdoor pools and they probably had CYA in them. If they had 30 ppm CYA, then it would take about 40 ppm FC to be equivalent to 10 ppm FC with no CYA. So I'm guessing that's how they got to their number.
Basically, Crypto is resistant to chlorine so I've been suggesting (to anyone who will listen) using, after a diarrhea incident, an alternative such as chlorine dioxide which is at least 10 times more powerful against Crypto and would only require an overnight closure at just a few ppm of chlorine dioxide. Unfortunately, the EPA won't allow this until studies are done (at $3-4 million) to prove that the byproducts (mostly chlorate and some chlorite) are in small enough quantities even though pool water is not used for drinking purposes.
Crypto is only passed on from infected persons so you aren't at any risk in your own pool unless you invite someone over who has diarrhea with Crypto. For public pools, it's a tough situation, though use of UV and microfiltration systems will help reduce the amount of exposure, though it takes multiple turnovers to clear the water. Cyrpto does not grow in pool water -- it is an oocyst, essentially a protozoa wrapped in a very tough shell in a dormant state. It's only when it gets into your mouth and into your intestines that it comes out and parties, so to speak.
Richard
