Legionnaires' disease associated with a hospital water system. A five-year progress report on continuous hyperchlorination
C. M. Helms, R. M. Massanari, R. P. Wenzel, M. A. Pfaller, N. P. Moyer and N. Hall
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City.
In 1981, sixteen cases of nosocomial legionellosis occurred among 456
patients admitted to a new hematology-oncology unit (35 per 1000
admissions). Monoclonal antibody typing and restriction endonuclease
plasmid analysis identified a unique strain (09,04) of Legionella
pneumophila serogroup 1 isolated from both patients and water outlets.
Continuous hyperchlorination of the hot and cold water began in January
1982, and chlorine levels of 3 to 5 mg/L have been maintained most
recently. Water samples have been consistently negative for Legionella for
more than five years. Four sporadic cases of nosocomial legionellosis have
occurred in the hematology-oncology unit during the same period (one per
1000 admissions) associated with a different strain of L pneumophila
serogroup 1 (09,00). The environmental reservoir(s) of L pneumophila
serogroup 1 in these cases has not been identified. Levels of
trihalomethanes (potential carcinogens) were high (greater than 100
micrograms/L) when chlorine levels of hot water exceeded 4 mg/L. Some
corrosion damage to the water distribution system has occurred: the average
number of leaks per month increased steadily from zero in 1982 to 5.2 in
1986. The chlorinator installation costs were +75,800, and annual operation
expenses were +12,500. Continuous hyperchlorination is a promising but
still experimental technique for control of nosocomial legionellosis. In
our experience, epidemic disease has been controlled, but sporadic cases
have continued to occur.
