Prevalence and Significance of Legionella pneumophila Contamination of Residential Hot-Tap Water Systems

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Abstract
A culture survey of hot-tap water systems in 95 apartments and houses in one area of Chicago showed that 30 (32%) were contaminated by Legionella pneumophila, ranging in concentration from 1 to 104 organisms/liter. Culture-positive and -negative systems differed significantly only in hot-tap water temperature (P < .005), which was L. pneumophila with positive tap water cultures. Virulence of selected tap water isolates of L. pneumophila in embryonated eggs was similar to that of clinical isolates. In the area studied, residential hot-tap water systems maintained at L. pneumophila, but systems with low levels of contamination (⩽104 organisms/liter) appear not to be an important source of infection of healthy individuals.