Factors predisposing to Legionella pneumophila colonization in residential water systems.

Fifty-five homes in the Pittsburgh area were surveyed for the presence of Legionella pneumophila colonization. Hot water tanks, faucets, and showerheads were sampled. Six homes yielded Legionella pneumophila within the water distribution system. Lower water temperatures (less than 48.8 degrees C) within the hot water system were significantly associated with the presence of L. pneumophila colonization. A similar association was found for electric heaters; however, this association may be an indirect one. Water temperatures in electrically heated tanks were significantly lower than in gas-heated tanks. City residences were also more likely to be colonized than suburban residences. Because acquisition of Legionnaires' disease in the community has been linked to colonization of the water supplies in the homes of affected patients, these findings may have clinical implications for susceptible individuals residing in homes with water supplies colonized by L. pneumophila.