Factors contributing to the contamination of hospital water distribution systems by legionellae.

To identify factors associated with the contamination of hospital water distribution systems by legionellae, 84 Quebec hospitals provided 3284 hot water specimens from 839 different sites. Concentrated samples were seeded on buffered charcoal yeast extract agar and a semi-selective medium. At least one water sample was contaminated by legionellae in 57 hospitals (67.9%). In 22 hospitals (26.2%), greater than 30% of samples were contaminated by these bacteria. In 9 (12.2%) of 74 hospitals, distilled water was colonized. The presence of at least one positive sample was found to be associated with localization and number of hospital beds (P = .02 for both). Heavy contamination was associated with large volume hot water tanks (P = .01), low water temperature at faucet (P = .03), and old water heaters (P = .06). Conditions required for the occurrence of nosocomial legionellosis may be present in numerous hospitals.