Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for source waters of 66 surface water treatment plants in 14 states and 1 Canadian province. The results showed that cysts and oocysts were widely dispersed in the aquatic environment. Giardia spp. were detected in 81% of the raw water samples. Cryptosporidium spp. were found in 87% of the raw water locations. Overall, Giardia or Cryptosporidium spp. were detected in 97% of the raw water samples. Higher cyst and oocyst densities were associated with source waters receiving industrial or sewage effluents. Significant correlations were found between Giardia and Cryptosporidium densities and raw water quality parameters such as turbidity and total and fecal coliform levels. Statistical modeling suggests that cyst and oocyst densities could be predicted on the basis of watershed and water quality characteristics. The occurrence of high levels of Giardia cysts in raw water samples may require water utilities to apply treatment beyond that outlined in the Surface Water Treatment Rule of the U.S. Environmental Protection Agency.

Rainfall increases concentrations of Giardia and Cryptosporidium through its influence on turbidity, flow volume, and possibly other unidentified factors. An investigation of the variability of concentrations of Giardia cysts and Cryptosporidium oocysts in the Delaware River was conducted in 1996 at Trenton, N.J. A goal of the study was to examine the relationship between concentrations of Giardia and Cryptosporidium and a variety of more easily measured microbial, water quality, and meteorological parameters. A positive correlation (Spearman rank; p < 0.05) was demonstrated between concentrations of Giardia cysts or Cryptosporidium oocysts and 15 other parameters. Increased concentrations of Giardia and Cryptosporidium as well as a variety of other microorganisms were associated with rainfall. The effect of rainfall on parasite concentrations is due in part to increased particulate matter in the water column following surface runoff and resuspension of river bottom and storm drain sediment.

Giardia and Cryptosporidium levels were determined by using a combined immunofluorescence test for ifitered drinking water samples collected from 66 surface water treatment plants in 14 states and 1 Canadian province. Giardia cysts were detected in 17% of the 83 filtered water effluents. Cryptosporidium oocysts, were observed in 27% of the drinking water samples. Overall, cysts or oocysts were found in 39% of the treated effluent samples. Despite the frequent detection of parasites in drinking water, microscopic observations of the cysts and oocysts suggested that most of the organisms were nonviable. Compliance with the filtration criteria outlined by the Surface Water Treatment Rule of the U.S. Environmental Protection Agency did not ensure that treated water was free of cysts and oocysts. The average plant effluent turbidity for sites which were parasite positive was 0.19 nephelometric turbidity units. Of sites that were positive for Giardia or Cryptosporidium spp., 78% would have been able to meet the turbidity regulations of the Surface Water Temperature Rule. Evaluation of the data by using a risk assessment model developed for Giardia spp. showed that 24% of the utilities examined would not meet a 1/10,000 annual risk of Giardia infection. For cold water conditions (0.5°C), 46% of the plants would not achieve the 1/10,000 risk level.

The D/DBP Rule and the ESWTR must be orchestrated carefully to ensure protection of public health. The American Water System has conducted extensive monitoring of its operations since 1988. Analysis of 347 surface water samples collected between 1988 and 1993 showed that the prevalence rate of Giardia and Cryptosporidium was 53.9 percent and 60.2 percent, respectively. But because the parasite assay does not indicate viability or virulence, these results do not necessarily indicate that these water systems were at risk from waterborne pathogens. To supplement coagulation and filtration, the average system will have to apply sufficient disinfection to reduce viable Giardia levels by 3.1 log10. An analysis of existing disinfection practices shows that most systems are already applying disinfectant at a level sufficient to reduce Giardia levels. However, the proposed Disinfectants/Disinfection By‐products (D/DBP) Rule may hamper the ability of water utilities to apply sufficient disinfection under current operating conditions. Careful integration of the D/DBP and the Enhanced Surface Water Treatment rule is encouraged.

The accurate determination of the presence of Giardia cysts and Cryptosporidium oocysts in surface waters requires a reliable method for the detection and enumeration of these pathogenic organisms. Published methods have usually reported recovery efficiencies of less than 50% for both cysts and oocysts. Typically, the losses are greater for Cryptosporidium oocysts than they are for Giardia cysts. The purpose of this study was to examine procedures used for sample collection, elution, concentration, and clarification to determine when losses of cysts and oocysts occurred during processing. The results showed that major losses of cysts and oocysts occurred during centrifugation and clarification. Depending on the centrifugation force, oocyst losses of as high as 30% occurred for each centrifugation step. A 1.15-specific-gravity Percoll-sucrose gradient was needed to optimize recovery of oocysts from natural water samples. Minor improvements in the procedure could be accomplished by selecting a filter other than the recommended 1-m-pore-size (nominal-porosity) polypropylene filter. Giardia cysts and Cryptosporidium oocysts are environmentally resistant intestinal parasites that can cause gastroenteritis in humans when they are ingested. These organisms can be transported by water and have caused documented waterborne outbreaks of giardiasis and cryptosporidiosis (6). The method of detection for Giardia cysts and Cryptosporidium oocysts in water samples relies primarily on microscopic observation of water samples by an immunofluorescence technique (1). This method involves filtration of a large volume of water through a 1-m-pore-size (nominal-porosity) cartridge filter, elution of the microorganisms from the filter using a detergent-based elution medium, concentration by centrifugation, clarification using a 1.10-specific-gravity Percoll-sucrose density gradient, indirect fluorescent-antibody labeling, and microscopic examination of the sample. The immunofluorescence assay (IFA) for Giardia cysts and Cryptosporidium oocysts is time-consuming and labor intensive and requires a large degree of analytical expertise. Moreover, the recovery efficiency of the procedure, especially for Cryptosporidium oocysts, is relatively low. LeChevallier et al. (5) reported an average method efficiency of 68.6% for Giardia cysts in seeded tap water; however, Cryptosporidium oocysts were recovered at an average level of only 25.3%. A recent study of 12 commercial laboratories that processed spiked proficiency samples showed an average of 9% recovery of Giardia cysts and 3% recovery of Cryptosporidium oocysts (2). Moreover, 36% failed to detect Giardia cysts and 55% failed to find Cryptosporidium oocysts, even though the samples contained 99 cysts and 80 oocysts. Large variations in recovery efficiencies have been reported between different laboratories and even within a single laboratory (2, 3). The objective of the present study was to analyze the IFA technique, to determine when the losses of cysts and oocysts occurred during sample pr...