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Abstract: A survey of Giardia and Cryptosporidium was conducted in surface water used as drinking water sources by public water systems in four densely urbanized regions of Sao Paulo State, Brazil. A Quantitative Microbial Risk Assessment, based on protozoa concentrations, was performed to estimate the probability of protozoa infection associated with drinking water ingestion. A total of 206 source water samples were analyzed over a 24month period using the USEPA Method 1623. The risk of infection was estimated using an exponential dose response model, children and adults exposure and a gamma distribution for (oo)cyst concentrations with three scenarios for treating censored data. Giardia was detected in 102 of the samples, and 19 of them were also positive for Cryptosporidium, with maximum concentrations of 97.0cysts/L and 6.0oocysts/L, respectively. Risk distributions were similar for the three scenarios. In the four regions, the estimated risk of Giardia infection per year, for adults and children, ranged from 0.29% to 2.47% and from 0.08% to 0.70%, respectively. Cryptosporidium risk infection varied from 0.15% to 0.29% for adults and from 0.04% to 0.08% for children. In both cases, the calculated risk surpassed the risk of infection of 10−4 (1:10,000) defined as tolerable by USEPA for a yearly exposure. The probability of Giardia infection was very close to the rates of acute diarrheic disease for adults (1% to 3%) but lower for children (2% to 7%). The daily consumption of drinking water was an important contributing factor for these differences. The Microbiological Risk Assessment carried out in this study provides an indication of infection risks by Giardia and Cryptosporidium in the population served by these source waters. Strategies for source water protection and performance targets for the water treatment should be established to achieve the required level of public health risk. [Copyright &y& Elsevier]

Surface water contaminated by domestic sewage discharges is a potential source of pathogens, including protozoa. During 2005-2006, the source water (Atibaia River) of the Surface Water Treatment Plant (WTP) of Campinas city, São Paulo, Brazil was sampled to obtain an assessment of Cryptosporidium oocyst and Giardia cyst concentrations. Calcium carbonate flocculation (CCF) and membrane filtration (MF) concentration techniques, with and without purification by immunomagnetic separation (IMS) were evaluated. The cysts and oocysts were detected by immunofluorescence assay (IFA) and confirmed by differential interference contrast (DIC). Membrane filtration method generally produced higher recovery efficiency. Giardia spp. was detected in 87.5% of the water samples analyzed with densities ranging from 2.5 to 120 cysts per L. Cryptosporidium spp were detected in 62.5% and the concentrations ranged from 15 to 60 oocysts per L. Cryptosporidium oocyst and Giardia cyst concentrations detected in this study were elevated and are associated with discharge of untreated sewage in Atibaia River. Measures should be taken to protect surface water from sources of contamination. [ABSTRACT FROM AUTHOR]