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J Water Health. 2008 Dec;6(4):513-20. doi: 10.2166/wh.2008.068.

Inactivation of Cryptosporidium parvum under chlorinated recreational water conditions.

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  • 1Division of Parasitic Diseases, Centers for Disease Control and Prevention, National Center for Infectious Disease, Atlanta, GA 30341-3724, USA.


Cryptosporidium is a chlorine-resistant protozoan parasite and the etiological agent in many disinfected recreational water outbreaks. While previous studies have reported disinfection Ct values for Cryptosporidium parvum using sodium hypochlorite, these studies have employed conditions and procedures which are not ideal for establishing public health remediation recommendations for chlorinated recreational water venues. In the present study, free chlorine Ct values were measured at pH 7.5 using young oocysts (<1 month old) and tissue culture to determine oocyst viability. Two different oocyst isolates were used: one originating from Iowa and one from Maine (USA). This study determined that the Ct values for a 3-log reduction in oocyst viability were 10,400 (Iowa) and 15,300 (Maine) at pH 7.5. These Ct values are higher than the Centers for Disease Control and Prevention (USA) currently recommends (Ct = 9,600) for achieving a 3.0-log inactivation of Cryptosporidium oocysts during remediation of recreational water venues following fecal diarrhea accidents.

Copyright IWA Publishing 2008.

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