Hi all…a review of “Epidemiological Studies of Drinking-Water Turbidity in Relation to Acute Gastrointestinal Illness” has been published in the journal Environmental Health Perspectives. The authors examined 14 published studies. Table 3 provides a summary of studies which investigated the association between turbidity of drinking water supplies and risk of acute gastrointestinal illness. In many cases the treatment train is identified. Treated water turbidities are provided for pre-outbreak conditions and during the estimated time of exposure. Figure 1 provides lag times between exposure and symptoms. This could be generally useful for utilities if a waterborne disease outbreak occurs in their service areas as lag times should be relatively similar for a given pathogen.
The authors conclude that “multiple time-series studies have observed an association between turbidity of drinking-water supplies and risk of AGI. Associations have been observed in unfiltered and filtered water systems and at levels of relatively high and low turbidity. The positive studies suggest an underlying risk of waterborne AGI during the time periods at which the systems were studied. Nevertheless, inconsistencies between the studies indicate that the utility of turbidity as a proxy for microbiological contamination may be context specific. The body of work demonstrates the efficacy of studies correlating turbidity with AGI counts in time-series for preliminary investigation of the safety of water supplies. The context-specific nature of the association between drinking-water turbidity and AGI suggests that future research will be most effective if strategized towards elucidating specific- rather than generalized associations.”
This is an open access publication so you should be able to download it if you are interested. https://ehp.niehs.nih.gov/ehp1090/
Bill
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Review of Epidemiological Studies of Drinking-Water Turbidity in Relation to Acute Gastrointestinal Illness
Anneclaire J. De Roos, Patrick L. Gurian, Lucy F. Robinson, Arjita Rai, Issa Zakeri, and Michelle C. Kondo
Environmental Health Perspectives Vol 25, No 8, 2017
https://ehp.niehs.nih.gov/ehp1090/
“Background: Turbidity has been used as an indicator of microbiological contamination of drinking water in time-series studies attempting to discern the presence of waterborne gastrointestinal illness; however, the utility of turbidity as a proxy exposure measure has been questioned.
Objectives: We conducted a review of epidemiological studies of the association between turbidity of drinking-water supplies and incidence of acute gastrointestinal illness (AGI), including a synthesis of the overall weight of evidence. Our goal was to evaluate the potential for causal inference from the studies.
Methods: We identified 14 studies on the topic (distinct by region, time period and/or population). We evaluated each study with regard to modeling approaches, potential biases, and the strength of evidence. We also considered consistencies and differences in the collective results
Discussion: Positive associations between drinking-water turbidity and AGI incidence were found in different cities and time periods, and with both unfiltered and filtered supplies. There was some evidence for a stronger association at higher turbidity levels. The studies appeared to adequately adjust for confounding. There was fair consistency in the notable lags between turbidity measurement and AGI identification, which fell between 6 and 10 d in many studies.
Conclusions: The observed associations suggest a detectable incidence of waterborne AGI from drinking water in the systems and time periods studied. However, some discrepant results indicate that the association may be context specific. Combining turbidity with seasonal and climatic factors, additional water quality measures, and treatment data may enhance predictive modeling in future studies. https://doi.org/10.1289/EHP1090 “
