STUDIES ON THE PREVALENCE OF GIARDIA CYSTS AND CRYPTOSPORIDIUM OOCYSTS IN SOUTH-AFRICAN WATER

The levels of Giardia cysts and Cryptosporidium oocysts in 650 environ mental water samples ere investigated. Cysts and oocysts were found in all types of water tested. The presence of Giardia cysts exceeded Cry ptosporidium oocysts both in the number per sample and the number of p ositive samples. Almost 50% of sewage samples studied contained Giardi a cysts and 30% contained both Giardia cysts and Cryptosporium oocysts . Treatment of sewage resulted in a reduction in the percentage of sam ples containing cysts and/or oocysts (30% of treated effluent samples were positive for Giardia and 25% had both cysts and oocysts). Higher numbers of Giardia cysts were found in surface water samples than in e ither sewage or treated effluents (55% of surface water samples were-p ositive). However, the number of cysts isolated per surface water samp le was lower on average. Most water purification plants showed effecti ve removal of cysts and oocysts. However, 13% of potable water samples contained protozoan parasites, indicating occasional failure of the p urification processes and the need for monitoring final treated water.