The effect of chlorination on the rates of gastroenteritis


Prof Christopher Fairley
Dr Margaret Hellard
Dr Martha Sinclair
Dr Shyamali Dharmage (Melbourne University)

Funded by: Melbourne Water Corporation

Disinfection of water supplies has led to a remarkable decline in gastrointestinal and other diseases in developed nations, beginning in late 19th century. Studies in the developing world have indicated that the effect of chlorination and improved sanitation together reduce the amount of gastroenteritis by up to eighty percent, although it is difficult to separately measure the effect of these two interventions.

In the past 10 to 15 years there has been increasing concern in industrialised countries about the risks associated with adding chlorine to our drinking water supply. Chlorine is used to kill potentially harmful microorganisms, which cause gastroenteritis and other diseases. The main concern is that the disinfection byproducts, that result when chlorine interacts with organic matter, may contribute to increased cancer risks or adverse pregnancy outcomes.

The evidence linking chlorine and its byproducts to adverse health effects is weak but nonetheless there is community concern surrounding this issue. Such community concerns over the possible adverse effects of disinfection byproducts are believed to have contributed to a reduction in the chlorination levels in water supplies in Peru which unfortunately resulted in a devastating outbreak of cholera . For this reason it is important to attempt to measure the benefits of chlorinating the water and to compare these benefits with the potential risks of chlorination.

This project assessed the impact of chlorination on gastroenteritis in the city of Melbourne by examining gastroenteritis morbidity and mortality figures in children for the interval spanning the introduction of chlorination. Melbourne's water is drawn from closed, protected catchments and for this reason, chlorine was not added to the water supply until the mid 1970's - much later than in most large cities in the developed world. Medical records in the mid 1970's are more accurate than medical records around the turn of the century. Therefore by using available records it may be possible to obtain an indication of the rates of gastroenteritis in Melbourne before and after chlorination of the water supply. If chlorine sensitive microorganisms in drinking water were a significant source of illness prior to chlorination, then a decrease in rates of gastroenteritis would be expected when chlorination was commenced.Childhood gastroenteritis was examined for two of the three indicators since it is accepted that the majority of gastroenteritis cases in children are attributable to infectious causes whereas gastroenteritis symptoms in adults may be due to a range of infectious and non-infectious illnesses.

The project has been completed and a report delivered to Melbourne Water Corporation. No significant change in rates of gastroenteritis was observed over the interval when water chlorination was introduced. This may indicate that waterborne disease represented a minor portion of community gastroenteritis at the time, or that the indicators measured here were too insensitive to detect a significant change in disease rates.

Hellard ME, Sinclair MI, Dharmage SC, Bailey MJ and Fairley CK (2002). The rate of gastroenteritis in a large city before and after chlorination. International Journal of Environmental Health Research 12 (4) 355-360.