Monochloramine and Legionnaires' disease

egionnaires’ disease was first recognized in 1976 during an outbreak among attendees at an American Legion convention. The disease is a form of pneumonia caused by bacteria of the genus Legionella. Legionella thrives at warm temperatures (25–42oC [77–108oF]). It lives inside biofilm in aquatic environments, usually as an intracellular parasite of amoebae.1 This lifestyle protects it from disinfectants, such as chlorine, that penetrate poorly into biofilm. Legionnaires’ disease occurs when a susceptible person inhales a Legionellacontaining aerosol. It also occurs less often through aspiration when a person drinks contaminated water. Showers, faucets, cooling towers, and many other devices can produce infectious aerosols. Legionnaires’ disease is caused by Legionella bacteria, which live in biofilm in natural and synthetic aquatic environments. The most frequent route of infection is inhalation of contaminated aerosol, which is often produced by faucets, showers, or cooling towers. Although the disease can be disseminated in potable water, the effects of the disinfection methods used by municipal water treatment facilities on the occurrence of Legionnaires’ disease have not been studied. This article describes an epidemiological study in which methods for disinfecting potable water supplied to 32 hospitals where outbreaks of Legionnaires’ disease have occurred are compared with methods for water supplied to 48 randomly selected control hospitals. Hospitals supplied with drinking water containing free chlorine were 10.2 times more likely to have reported an outbreak of Legionnaires’ disease associated with potable water than hospitals that used water with monochloramine as a residual disinfectant (odds ratio—10.2; 95 percent confidence interval—1.4–460). For executive summary, see page 180. PAT H O G E N S