We evaluated data from 10 laboratories that analyzed water samples from 82 recreational water sites across the state of Michigan between 2016 and 2018. Water sample replicates were analyzed by experienced U.S. Environmental Protection Agency (EPA) analysts and Michigan laboratories personnel, many of whom were newly trained, using EPA Draft Method C—a rapid quantitative polymerase chain reaction (qPCR) technique that provides same day Escherichia coli (E. coli) concentration results. Beach management decisions (i.e. remain open or issue an advisory or closure) based on E. coli concentration estimates obtained by Michigan labs and by the EPA were compared; the beach management decision agreed in 94% of the samples analyzed. We used the Wilcoxon one-sample signed rank test and nonparametric quantile regression to assess (1) the degree of agreement between E. coli concentrations quantified by Michigan labs versus the EPA and (2) Michigan lab E. coli measurement precision, relative to EPA results, in different years and water body types. The median quantile regression curve for Michigan labs versus EPA approximated the 1:1 line of perfect agreement more closely as years progressed. Similarly, Michigan lab E. coli estimates precision also demonstrated yearly improvements. No meaningful difference was observed in the degree of association between Michigan lab and EPA E. coli concentration estimates for inland lake and Great Lakes samples (median regression curve average slopes 0.93 and 0.95, respectively). Overall, our study shows that properly trained laboratory personnel can perform Draft Method C to a degree comparable with experienced EPA analysts. This allows health departments that oversee recreational water quality monitoring to be confident in qPCR results generated by the local laboratories responsible for analyzing the water samples.

我们评估了10个实验室的数据，这些实验室分析了2016年至2018年密歇根州82个休闲用水场所的水样。美国经验丰富的美国环境保护署（EPA）分析人员和密歇根实验室的工作人员对水样重复进行了分析，其中许多人是新来的使用EPA草案方法C进行了培训，该方法是一种快速定量聚合酶链反应（qPCR）技术，可提供当日大肠杆菌（E. coli）的浓缩结果。基于大肠杆菌的海滩管理决策（即保持开放或发出咨询或关闭通知）比较了密歇根实验室和EPA获得的浓度估计值；94％的分析样本同意海滩管理决策。我们使用Wilcoxon一样本带符号秩检验和非参数分位数回归来评估（1）密歇根实验室相对于EPA量化的大肠杆菌浓度之间的一致性程度，以及（2）相对于EPA的密歇根实验室大肠杆菌的测量精度结果，在不同的年份和水体类型。随着时间的推移，密歇根州实验室与EPA的中位数分位数回归曲线更加接近1：1完美一致曲线。同样，密歇根实验室的大肠杆菌估计精度也显示出逐年提高。对于内陆湖泊和大湖地区的样本，密歇根实验室与EPA大肠杆菌浓度估计值之间的关联度没有观察到有意义的差异（中位数回归曲线平均斜率分别为0.93和0.95）。总体而言，我们的研究表明，受过良好培训的实验室人员可以按照与经验丰富的EPA分析人员相当的程度执行C法草案。这使负责娱乐水质监测的卫生部门对负责分析水样的当地实验室产生的qPCR结果充满信心。