tgmb said:
Yes, I would try not to make it a habit of inviting feverish diarrheal people over for swim parties....
:
Symptoms may last for up to two weeks, though they may come and go sporadically for up to a month, even in people with healthy immune systems. Some people with cryptosporidium infection may have no symptoms."
If one has Crypto without symptoms and that includes not having diarrhea, then one is not as likely to be releasing oocysts into the water in great numbers (and they do not multiply in the water; they require hosts). Having the host get diarrhea is part of the normal life cycle for that organism -- it's the way to force oocysts into a watery environment to find another host.
Again, not a single report of Crypto in residential pools. In
this report, at the end of the swim season samples were taken from 160 public swimming pools in Atlanta, GA, 6.2% tested positive for
Giardia intestinalis while 1.2% test positive for
Cryptosporidium spp.. Crypto is the leading cause of intestinal illness from public pools because it is very chlorine-resistant. In pools improperly treated with chlorine (i.e. with very low or zero FC levels), many other pathogens can cause illness so while chlorine has significantly lowered the total illness rate, what is leftover is mostly from Crypto.
I noted
Giardia lamblia (intestinalis) which is also a protozoan cyst in pool water but though chlorine resistant, it is not nearly as resistant as Crypto.
Clostridium difficile is different in that it is not a protozoa and is an anaerobic bacteria, but it does go through a spore stage and is shed through feces. The CT value for 3-log reduction (99.9%) for Crypto oocysts is 15,300 while for Giardia cysts it is 45 and for Clostridium spores it is about 45,000 (based on Rutala, 2006 showing 4-log reduction in 10-20 min. with 6000 ppm hypochlorite). So Clostridium in pools would be even more resistant to chlorine than Cryptosporidium, but I couldn't find info on the number of spores needed for infection, but as described in
this link, C. difficile can be found in the stools of over half of children under 2 years old and of 5% of healthy adults. Healthy people rarely develop symptoms of C. difficile infection because other bacteria normally present in the intestine prevent C. difficile germs from multiplying.