A field study of the survival of Legionella pneumophila in a hospital hot-water system.

The colonization, survival and control of Legionella pneumophila in a hospital hot-water system was examined. The organism was consistently isolated from calorifier drain-water samples at temperatures of 50 degrees C or below, despite previous chlorination of the system. When the temperature of one of two linked calorifiers was raised to 60 degrees C, by closing off the cold-water feed, the legionella count decreased from c. 10(4) c.f.u./l to an undetectable level. However, 10 min after turning on the cold-water feed which produced a fall in calorifier temperature, the count in the calorifier drain water returned to its original level. Investigations revealed that the cold-water supply was continually feeding the calorifiers with L. pneumophila. Simple modifications in the design of the system were made so that the cold-water feed no longer exceeds 20 degrees C; these measures have considerably reduced the number of L. pneumophila reaching the calorifiers.