van Lieverloo J Hein M, Blokker E J Mirjam, Medema Gertjan
Kiwa Water Research, Groningenhaven 7 PO Box 1072, 3430 BB, Nieuwegein, The Netherlands.
J Water Health. 2007;5 Suppl 1:131-49. doi: 10.2166/wh.2007.134.
Quantitative Microbial Risk Assessments (QMRA) have focused on drinking water system components upstream of distribution to customers, for nominal and event conditions. Yet some 15-33% of waterborne outbreaks are reported to be caused by contamination events in distribution systems. In the majority of these cases and probably in all non-outbreak contamination events, no pathogen concentration data was available. Faecal contamination events are usually detected or confirmed by the presence of E. coli or other faecal indicators, although the absence of this indicator is no guarantee of the absence of faecal pathogens. In this paper, the incidence and concentrations of various coliforms and sources of faecal contamination were used to estimate the possible concentrations of faecal pathogens and consequently the infection risks to consumers in event-affected areas. The results indicate that the infection risks may be very high, especially from Campylobacter and enteroviruses, but also that the uncertainties are very high. The high variability of pathogen to thermotolerant coliform ratios estimated in environmental samples severely limits the applicability of the approach described. Importantly, the highest ratios of enteroviruses to thermotolerant coliform were suggested from soil and shallow groundwaters, the most likely sources of faecal contamination that are detected in distribution systems. Epidemiological evaluations of non-outbreak faecal contamination of drinking water distribution systems and thorough tracking and characterisation of the contamination sources are necessary to assess the actual risks of these events.
定量微生物风险评估（QMRA）主要关注向客户供水的分配系统上游的饮用水系统组件，包括正常情况和事故情况。然而，据报道，约15%-33%的水源性疾病暴发是由分配系统中的污染事件引起的。在大多数此类情况下，可能在所有非暴发污染事件中，都没有病原体浓度数据。粪便污染事件通常通过大肠杆菌或其他粪便指示菌的存在来检测或确认，尽管没有这种指示菌并不能保证不存在粪便病原体。在本文中，利用各种大肠菌群的发生率和浓度以及粪便污染来源来估计粪便病原体的可能浓度，进而估计受事件影响地区消费者的感染风险。结果表明，感染风险可能非常高，尤其是弯曲杆菌和肠道病毒引起的风险，但不确定性也非常高。在环境样本中估计的病原体与耐热大肠菌群比例的高度变异性严重限制了所述方法的适用性。重要的是，土壤和浅层地下水中肠道病毒与耐热大肠菌群的比例最高，而这些是在分配系统中检测到的最可能的粪便污染来源。对饮用水分配系统非暴发粪便污染进行流行病学评估，并对污染源进行全面跟踪和特征分析，对于评估这些事件的实际风险是必要的。
