AWWA PATH50805

In this study four in vitro viability assays (excystation, DAPI/PI, SYTO(R)-9 and SYTO(R)-59) were compared with CD-1/ICR neonatal mouse infectivity, following partial oocyst inactivation using low levels of pulsed ultraviolet (UV) light or following small contact times with low concentrations of ozone. Each disinfection study was conducted sequentially in the US and United Kingdom, using the same batch of the Iowa isolate and indicated high levels of variability with all four viability assays and infectivity assays also. In vitro assays demonstrated presence of viable oocysts following UV or ozone treatment of fresh and aged oocysts. In contrast, UV treatment yielded no infection (with inocula up to 500 oocysts), whereas ozonated oocysts yielded variable levels of infection (with three different inocula) at 7 days post-infection. Comparison of in vitro data (by each of the four viability assays) with mouse infectivity data indicated both UV or ozone treatment resulted in excystation, DAPI/PI, SYTO(R)-9 and SYTO(R)-59 over-estimating viability when compared to mouse infectivity. These data indicate that caution needs to be exercised when interpreting the significance of disinfection data generated with these in vitro assays following oocyst exposure to low levels of UV or ozone. Includes 11 references, figures.

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Edition:

Vol. - No.

Published:

08/29/1999

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1 file , 110 KB