Endemic Legionellosis Uncovered in a Prospective Study of Hospital-Acquired Legionnaires' Disease: Value of Environmental Monitoring

Abstract

BACKGROUND: Hospital-acquired Legionnaires' disease (LD) has a fatality rate of 28%, and the source is the water distribution system. The CDC approach to prevention emphasizes clinical surveillance for disease without environmental monitoring. The Pittsburgh approach recommends environmental monitoring even in the absence of known cases of LD. We determined the Legionella colonization status of water systems in 20 U.S. hospitals without known endemic hospital-acquired LD. METHODS: Twenty hospitals (in 13 states) performed clinical and environmental surveillance for Legionella from 2000 and 2002. RESULTS: Legionella pneumophila (Lp) and L. anisa were isolated from 70% (14/20) and 45% (9/20) of hospital water systems, respectively. Of the environmental samples, 29% (198/676) tested positive for Legionella spp. More than 30% of distal outlets were positive for L. pneumophila in 43% (6/14) of the hospitals. L. pneumophila, serogroup 1 (Lp-1) was detected in 5/6 of these hospitals, while 1/6 hospitals was colonized with Lp serogroup 5. Patients were evaluated for LD from 12/20 hospitals: 377 of the 633 by urinary antigen and 577 by sputum culture. Hospital-acquired LD due to Lp-1 was only identified in hospitals with Lp-1 in >30% of distal outlets (80%, or 4/5, of hospitals); 1/5 hospitals were colonized with a monoclonal subtype of Lp-1 known to be less virulent. No cases of disease due to other serogroups or species (L. anisa) were identified. CONCLUSION: Environmental monitoring followed by clinical surveillance was successful in uncovering previously unrecognized cases of hospital-acquired LD.