Legionella spp. in a hospital hot water system: effect of control measures

Potential sources of Legionella spp. in a university hospital were investigated over 3 years in order to gain better understanding of the ecology and transmission of this organism to hospitalized patients. The survey highlighted the contamination of the hot water system with high concentrations of legionellas (up to 10(6) cfu 1(-1]. Legionella pneumophila serogroup 6 was predominant followed by L. pneumophila serogroup 10. Serogroup 1 and other species (L. longbeachae, L. micdadei) were rarely isolated. Serogroup 6 was also the predominant cause of nosocomial legionellosis in 15 sporadic cases in immunocompromised patients from 1981 to 1987. In light of this problem, several control measures were tried consecutively. A disinfection cycle with 6 ppm free chlorine failed to eradicate legionellas because of difficulties with the plumbing system. Raising the temperature in hot water tanks to 80 degrees C was effective locally, but mixer tanks where cold and hot water (60-65 degrees C) are mingled in order to achieve 45 degrees C became the principal reservoirs. Disconnecting the mixer tanks, maintaining a temperature of 60 degrees C in the heating tanks and accelerating the flow rate in the hot water system proved to be the most useful measures.