Role of stagnation and obstruction of water flow in isolation of Legionella pneumophila from hospital plumbing

Survival and multiplication of Legionella pneumophila in municipal drinking water systems

Studies were conducted to investigate the survival and multiplication of Legionella spp. in public drinking water supplies. An attempt was made, over a period of several years, to isolate legionellae from a municipal system. Sampling sites included the river water supply, treatment plant, finished water reservoir system, mains, and distribution taps. Despite the use of several isolation techniques, Legionella spp. could not be detected in any of the samples other than those collected from the river. It was hypothesized that this was due to the maintenance of a chlorine residual throughout the system. To investigate the potential for Legionella growth, additional water samples, collected from throughout the system, were dechlorinated, pasteurized, and inoculated with Legionella pneumophila. Subsequent growth indicated that many of these samples, especially those collected from areas affected by an accumulation of algal materials, exhibited a much greater ability to support Legionella multiplication than did river water prior to treatment. Chemical analyses were also performed on these samples. Correlation of chemical data and experimental growth results indicated that the chemical environment significantly affects the ability of the water to support multiplication, with turbidity, organic carbon, and certain metals being of particular importance. These studies indicate that the potential exists for Legionella growth within municipal systems and support the hypothesis that public water supplies may contaminate the plumbing systems of hospitals and other large buildings. The results also suggest that useful methods to control this contamination include adequate treatment plant filtration, maintenance of a chlorine residual throughout the treatment and distribution network, and effective covering of open reservoirs.

Potential in-hospital modes of transmission of Legionella pneumophila. Demonstration experiments for dissemination by showers, humidifiers, and rinsing of ventilation bag apparatus

The mode of transmission of nosocomial legionellosis remains uncertain. Aerosolization of Legionella pneumophila by showers, humidifiers, and respiratory equipment rinsed in tap water was evaluated using plate-settling culture and air aspirator methods. All protocols simulated the actual hospital setting including use of humidifier equipment used in hospital patient rooms and water from faucets and showerheads in hospitals with nosocomial Legionnaires' disease. Protocols for humidifier and shower experiments mimicked the procedure actually used in hospitals by health care personnel. Showering failed to produce aerosols of L. pneumophila; however, portable humidifiers readily generated aerosols of L. pneumophila that disseminated throughout a two-bed patient room. Intensity of aerosolization directly correlated with the degree of L. pneumophila contamination of the tap water used to fill the humidifier. Rinsing of ventilation bag apparatus with tap water led to isolation of L. pneumophila from culture plates after the ventilation bags were squeezed. Thus, L. pneumophila could be aerosolized or directly instilled into a patient's bronchial tree following routine measures for cleaning ventilation bag apparatus with tap water. On the basis of these results, the use of humidifiers filled with tap water has been discontinued and sterile water is recommended for rinsing ventilation bag apparatus and tubing.