THE DETECTION OF CRYPTOSPORIDIUM OOCYSTS AND GIARDIA CYSTS IN CISTERNWATER IN THE US VIRGIN-ISLANDS

Most homes and public facilities in the U.S. Virgin Islands use a roof catchment system to obtain drinking water. Because water is so scarce throughout the islands, every building (except those federally owned) are required to have a cistern. Rainwater is collected in the cistern s and is subject to contamination from enteric pathogens found in the environment. The objective of this study was to determine the occurren ce and concentrations of human enteric protozoa in cisterns originatin g from animal fecal contamination. Volumes of 4001 of water were filte red from nine private and four public cisterns four times over a 1-yea r period for a total of 44 samples. After processing the Alter, the en tire volume was examined using Cryptosporidium and Giardia specific an tibodies and epifluorescence microscopy to determine levels of Cryptos poridium oocysts and Giardia cysts. One or both of the protozoa were f ound in 81% of the public cisterns and this was statistically signific ant (P = 0.005) when compared to the private cisterns where 47% of the samples were positive. Cryptosporidium was found statistically more o ften in the 44 samples than Giardia. In addition, the use of a polyclo nal antibody for Cryptosporidium which is genera-specific, also detect ed oocysts statistically more often than a monoclonal antibody which w as more species-restrictive to C. parvum, which is associated with dis ease in humans, suggesting that non-mammalian oocysts were found more frequently in cistern waters. Levels ranged from 1 to 10 organisms/100 1 with one sample at 70 oocysts. These levels are associated with esti mated daily risks of 10(-2) to 10(-4) and are well above acceptable gu idance as described for safe drinking water in the United States. On o ccasion high levels of heterotrophic bacteria (9.9 x 10(5) CFU/ml) and total coliforms (> 2000 CFU/100 ml) were also detected in these water s. A statistically significant correlation was found between the detec tion of Cryptosporidium spp. and Giardia spp. (r = 0.47853, P = 0.0008 ). The results of this study show that Cryptosporidium and Giardia, as well as bacteria, are present in these waters at levels which may inv olve significant public health risks. Public cistern systems are of pa rticular concern because of the high percentage which were contaminate d and the greater number of people exposed.