Comparative survival of Cryptosporidium, coxsackievirus A9 and Escherichia coli in stream, brackish and sea waters.

Discharge of inadequately treated wastewater into streams may result in the dissemination of pathogens and the contamination of surface water sources. Determining the die-off rate of pathogenic microorganisms in stream and sea waters may serve as the basis for evaluating the health risks posed by the presence of pathogens in seawater. This study was conducted to determine the effect of microbial load, temperature, salinity and turbidity on the die-off of oocysts of Cryptosporidium as compared to that of coxsackie A9 virus (Cox A9) and E. coli. The test microorganisms were seeded into stream, outfall or sea waters and incubated at either 30 degrees C (summer) or 15 degrees C (winter). At 30 degrees C, the fastest die-off was observed for Cox A9 where < 5-log was reduced regardless of the water quality. At 1 degrees C Cox A9 persistence was similar to that of Cryptosporidium where no change was detected in the concentration of either throughout the study period. E. coli die-off reached 5 orders of magnitude within 10d then its concentration remained unchanged. The die-off of E. coli was faster than observed for Cox A9 at 15 degrees C regardless of the water quality. No decrease was observed in the viability of Cryptosporidium under all tested conditions throughout the study period indicating the unsuitability of E. coli to serve as an indicator for the presence of parasites and viruses in stream and marine waters. The prolonged persistence of pathogenic microorganisms in marine waters suggested that discharge of contamination into streams may present a serious environmental health risk.