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123 reported detection of poliovirus in waters with chlorine concentrations greater than 1 mg/L and turbidities less than 1.0 NTU, which indicates that protection from disinfection occurs even at very low turbidity levels. Although a study of 16 U.S. cities in 1961 failed to reveal a clearly defined relationship between hepatitis incidence and finished water turbidity, the authors stated that, because of the many factors involved, it should not be inferred that there is none.124 The infectious hepatitis epidemic in Delhi, India, occasioned by the massive contamination of the raw water source of a treatment plant by sewage, was also accompanied by a significant increase in raw water turbidity. Even though chlorination was practised, it was apparently insufficient to inactivate the infectious hepatitis virus.125 The protection from disinfection offered by organic or cellular material in particular has been reported in other studies.19,21
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