CETESB - Companhia Ambiental do Estado de Sao Paulo, Av. Prof. Frederico Hermann Jr., 345, São Paulo, SP 05459-900, Brazil.
Sci Total Environ. 2013 Jan 1;442:389-96. doi: 10.1016/j.scitotenv.2012.09.077. Epub 2012 Nov 22.
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.
对巴西圣保罗州四个城市化程度较高地区的公共供水系统所使用的地表水进行了贾第鞭毛虫和隐孢子虫调查。基于原生动物浓度进行了定量微生物风险评估，以估计与饮用水摄入相关的原生动物感染的可能性。在 24 个月的时间里，使用美国环保署方法 1623 对总共 206 个水源样本进行了分析。使用指数剂量反应模型、儿童和成人暴露以及（oo）囊泡浓度的伽马分布来估计感染风险，并针对处理截尾数据的三种情况。在 102 个样本中检测到了贾第鞭毛虫，其中 19 个样本也对隐孢子虫呈阳性，最大浓度分别为 97.0 个囊泡/L 和 6.0 个囊泡/L。在三种情况下，风险分布都相似。在四个地区，成人和儿童每年感染贾第鞭毛虫的估计风险分别为 0.29%至 2.47%和 0.08%至 0.70%。成人感染隐孢子虫的风险为 0.15%至 0.29%，儿童为 0.04%至 0.08%。在这两种情况下，计算出的风险都超过了美国环保署定义的可容忍的 10(-4)（1:10,000）感染风险，即每年暴露一次。贾第鞭毛虫感染的概率非常接近成人急性腹泻病的发生率（1%至 3%），但对儿童来说较低（2%至 7%）。饮用水的日消耗量是造成这些差异的一个重要因素。本研究进行的微生物风险评估表明，这些水源供水人群存在贾第鞭毛虫和隐孢子虫感染的风险。应制定水源保护策略和水处理绩效目标，以实现所需的公共卫生风险水平。
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