Volume 100, Issue 4     April 2008    ISSN 1551-8833

Legionnaires’ disease is a type of pneumonia caused by freshwater bacteria of the genus Legionella. Previous studies have shown that monochloramine disinfection of municipal water supplies is associated with decreased risk of Legionnaires’ disease transmitted in healthcare settings.

The authors performed a two-year, prospective environmental study to determine whether converting from chlorine to monochloramine for water disinfection would decrease Legionella colonization of hot water systems. Results of the study showed a significant reduction. Legionella colonized 60% of the hot water systems before monochloramine conversion versus 4% after conversion. These findings suggest that monochloramine in drinking water provides better control of Legionella growth in building plumbing systems than does chlorine. Although control of Legionnaires’ disease is unlikely to be a major factor in a water utility’s decision to convert to monochloramine for residual disinfection, if water suppliers convert to monochloramine to reduce concentrations of disinfection by-products, control of the growth of Legionella in potable water systems may be an additional health benefit.—MKK