Monochloramine and Legionnaires' disease - (Reprinted from Lancet, vol 353, pg 272, 1999)

Legionnaires' disease is caused by Legionella bacteria, which live in biofi lm in natural and synthetic aquatic environments. The most frequent route o f infection is inhalation of contaminated aerosol, which is often produced by faucets, showers, or cooling towers. Although the disease can be dissemi nated in potable water, the effects of the disinfection methods used by mun icipal water treatment facilities on the occurrence of Legionnaires' diseas e have not been studied. This article describes an epidemiological study in which methods for disinfecting potable water supplied to 32 hospitals wher e outbreaks of Legionnaires' disease have occurred are compared with method s for water supplied to 48 randomly selected control hospitals. Hospitals s upplied with drinking water containing free chlorine were 10.2 times more l ikely to have reported an outbreak of Legionnaires' disease associated with potable water than hospitals that used water with monochloramine as a resi dual disinfectant (odds ratio-10.2; 95 percent confidence interval-1.4-460) .