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Volume 5, Number 4—August 1999

Dispatch

Chlorine Disinfection of Recreational Water for Cryptosporidium parvum

Colleen Carpenter*, Ronald Fayer*Comments to Author , James Trout*, and Michael J. Beach†
Author affiliations: *U.S. Department of Agriculture, Beltsville, Maryland, USA and †Centers for Disease Control and Prevention, Atlanta, Georgia, USA

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Table 2

Contact times and infectivity for purified Crytosporidium parvum oocysts subjected to chlorination (Experiments 1 and 2)a

2 ppm
10 ppm
Infectivity
Infectivity
Expt. Days (min.) Ctb value 20ºC 30ºC Ctb value 20ºC 30ºC
2 (360) 720 4/4 4/4 3,600 4/4 0/4
2 (720) 1,440 4/4 3/4 7,200 0/4 0/4
1 1 (1440) 2,880 4/4c 0/4 14,400 0/4 0/4
2 1 (1440) 2,880 4/4 0/4 14,400 0/4 0/4
1 2 (2880) 5,760 0/4 0/4 28,800 0/4 0/4
2 2 (2880) 5,760 0/4 0/4 28,800 0/4 0/4
1 3 (4320) 8,640 4/4 0/4 43,200 0/4 0/4
2 3 (4320) 8,640 0/4 0/4 43,200 0/4 3/4
1 4 (5760) 11,520 0/4 0/4 57,600 0/4 0/4
1 5 (7200) 14,400 0/4 0/4 72,000 0/4 0/4
1 6 (8640) 17,280 0/4 0/4 86,400 0/4 0/4
1 7 (10,080) 20,160 0/4 0/4 100,800 0/4 0/4

aTreatments in which mice were found infected are shown in bold
bHypothetical Ct value calculated by assuming constant chlorine concentration.
cFraction represents number of mice showing developmental stages of C. parvum in the intestinal epithelium over the total number of mice inoculated, e.g., 4/4 indicates 4 mice were found infected out of 4 mice inoculated.

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