CDC DATA ON BASAL CHLORINE-RESISTANT PATHOGENS. “Enteroviruses have moderate chlorine tolerance, while Protozoa have high tolerance to chlorine. Notably, those with higher resistance, particularly toxoplasma and cryptosporidium, need long (1440 and 90 minute) chlorine exposures to achieve a 99% kill rate.”
http://www.cdc.gov/safewater/effectiveness-on-pathogens.html