There has been one study of the correlation of sales of diarrhea remedies with turbidity of drinking water (Beaudeau et al., 1999). The goal of this study was to assess whether drinking water turbidity (which water companies measure routinely) correlates with gastrointestinal illness in the community served by the water supply. Beaudeau and colleagues analyzed the correlation of daily water turbidity measurements with the daily sales of diarrhea remedies for a three-year period in Le Havre, France. There were no known outbreaks of cryptosporidiosis or other gastrointestinal illnesses during the period of the study.
They found that there were two 3-week periods of increases in sales of diarrhea remedies following two increases in water turbidity. Additionally, they found a statistically significant increase in sales of diarrhea remedies three to eight days after an interruption in the chlorination of water. They estimated that approximately 10% of annual cases of gastrointestinal illness were due to consumption of tap water. We note that they studied a combination of both prescription and OTC diarrhea remedies. However, only 20% of sales were of prescription diarrhea remedies, a proportion unlikely to have accounted for the entire effect.
Although it is possible that the correlation they observed was coincidental, other studies have analyzed the relationship between water turbidity and health indicators (other than OTC sales) and found similar correlations (Schwartz et al., 2000, Schwartz et al., 1997, Morris et al., 1996). A randomized, prospective epidemiological study found that individuals drinking tap water had a 14-19% higher incidence of gastrointestinal illness than individuals drinking purified bottled water (Payment et al., 1997), lending additional support to a real association between turbidity (presumably reflecting inadequate processing of source water that is a reservoir of one or more pathogens) and disease.
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