title: Assessing the infection risk of Giardia and Cryptosporidium in public drinking water delivered by surface water systems in Sao Paulo State, Brazil.
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 24 month 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 97.0 cysts/L and 6.0 oocysts/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.
authors.affiliation: CETESB - Companhia Ambiental do Estado de Sao Paulo, Av. Prof. Frederico Hermann Jr., 345, São Paulo, SP 05459-900, Brazil. minesato@sp.gov.br
authors.forename: Maria Ines Z
authors.initials: MI
authors.lastname: Sato
authors.forename: Ana Tereza
authors.initials: AT
authors.lastname: Galvani
authors.forename: Jose Antonio
authors.initials: JA
authors.lastname: Padula
authors.forename: Adelaide Cassia
authors.initials: AC
authors.lastname: Nardocci
authors.forename: Marcelo de Souza
authors.initials: Mde S
authors.lastname: Lauretto
authors.forename: Maria Tereza Pepe
authors.initials: MT
authors.lastname: Razzolini
authors.forename: Elayse Maria
authors.initials: EM
authors.lastname: Hachich
mesh_terms: D001938:Brazil; D003457:Cryptosporidiosis / Q000453:epidemiology / Q000382:microbiology / Q000517:prevention & control*; D003458:Cryptosporidium / Q000302:isolation & purification*; D060766:Drinking Water / Q000469:parasitology* / Q000592:standards; D005618:Fresh Water / Q000469:parasitology*; D005872:Giardia / Q000302:isolation & purification*; D005873:Giardiasis / Q000453:epidemiology / Q000382:microbiology / Q000517:prevention & control*; D006801:Humans; D009010:Monte Carlo Method; D011156:Population Density; D018570:Risk Assessment; D014507:Urbanization; D018508:Water Purification / Q000379:methods
chemical_list: D060766:Drinking Water