Control of Legionella in Drinking Water Systems: Impact of Monochloramine

Abstract

Legionella and Legionella-like organisms live as facultative intracellular parasites of amoebae in the biofilm that covers the inside of tanks and pipes in water systems. Recent investigations, discussed in this chapter, indicate that it is possible to prevent 90% of drinking-water-associated Legionnaires' disease (community acquired as well as nosocomial; sporadic disease as well as outbreaks) through the use of monochloramine for residual municipal water disinfection. Monochloramine (combined chlorine) is formed when ammonia and free chlorine are mixed in water in the correct ratio. Recent research has shown that monochloramine may be considerably more effective against Legionella and Legionella-like organisms than free chlorine. An interesting hypothesis is that monochloramine may also be better at killing the amoebae that serve as hosts to Legionella and Legionella-like organisms. To this author's knowledge, monochloramine is the only disinfectant that has been shown to reduce the incidence of Legionnaires' disease when used at the municipal level. This finding is not just important for control of nosocomial infections. More than 75% of cases of Legionnaires' disease acquire their infection in the community. Residual disinfection of municipal drinking water with monochloramine seems an inexpensive and efficient way to prevent many of these cases. In addition, supplemental injection of monochloramine may become one of the preferred methods for control of Legionella and Legionella-like organisms in hospitals, hotels, and similar institutions.