Effect of monochloramine disinfection of municipal drinking water on risk of nosocomial Legionnaires' disease

Background Many Legionella infections are acquired through inhalation or aspiration of drinking water. Although about 25% of municipalities in the USA use monochloramine for disinfection of drinking water. the effect of monochloramine on the occurrence of Legionnaires' disease has never been studied. Methods We used a case-control study to compare disinfection methods for drinking water supplied to 32 hospitals that had had outbreaks of Legionnaires' disease with the disinfection method for water supplied to 48 control-hospitals, with central for selected hospital characteristics and water treatment factors. Findings Hospitals supplied with drinking water containing free chlorine as a residual disinfectant were more likely to have a reported outbreak of Legionnaires' disease than those that used water with monochloramine as a residual disinfectant (odds ratio 10.2 [95% CI 1.4-460]), This result suggests that 90% of outbreaks associated with drinking water might not have occurred if monochloramine had been used Instead of free chlorine for residual disinfection (attributable proportion 0.90 [029-1.00]). Interpretation The protective effect of monochloramine against legionella should be confirmed by other studies. Chloramination of drinking water may be a cost-effective method for control of Legionnaires' disease at the municipal level or in individual hospitals, and widespread implementation could prevent thousands of cases.