Inactivation of Cryptosporidium parvum Oocysts by Ammonia

Volume 64, no. 2, p. 784–788, 1998. p. 786, Table 1. Table 1 should read as shown below.

TABLE 1.

Inactivation rates of C. parvum oocysts exposed to measured concentrations of ammonia^a

[NH3] (mol/liter)	K ± 95% CI/hb	Days to reach 99.999% inactivationc
0.007	0.014 ± 0.004	34.3
0.026	0.027 ± 0.007	17.8
0.039	0.050 ± 0.005	9.6
0.060d	0.047 ± 0.014	10.2
0.104	0.059 ± 0.034	8.1
0.148	0.066 ± 0.030	7.3
5.8e	0.479	1

^aBased on data from the dye permeability assay after a 24-h exposure. 

^bIt was assumed that oocyst inactivation was a first-order process. The coefficient of inactivation was determined by regressing ln (P₀/P_t) against time (derived from the equation P_t = P₀ · e^−Kt, where P₀ is the initial percentage of viable oocysts, P_t is the percentage of viable oocysts at time t, in hours, and K is the coefficient of inactivation). The 95% confidence intervals (CI) were determined by multiplying the Student t value at the appropriate degree of freedom and at an α level (two-sided) of 0.025 by the standard deviations of K. 

^cCalculated by the equation t = ln (P₀/P_t)/K. 

^dThis concentration of NH₃ and exposure time were used in the validation experiment shown in Table 2. 

^eA power function, y = 2.523x^−0.525 (r² = 0.993), that fit the regression of [NH₃] against days to reach 99.999% inactivation was used to determine the concentration of ammonia that would reduce the viability of oocysts by 99.999% in 1 day. The K value for this concentration of ammonia was then derived. 

Page 787, column 2, line 9: “26.5 days” should read “55.1 days.”