NOSOCOMIAL LEGIONNAIRES-DISEASE - ASPIRATION AS A PRIMARY-MODE OF DISEASE ACQUISITION

PURPOSE. Nosocomial Legionnaires, disease remains a significant proble m with many unresolved questions regarding transmission of legionella organisms to patients. We performed a case-control and environmental s tudy to identify risk factors and modes of transmission of Legionella infection during an outbreak of nosocomial Legionnaires` disease in a military medical center. PATIENT`S AND METHODS: During the calendar ye ar 1989, 14 cases of nosocomial Legionnaires' disease were identified by active surveillance following the discovery of 2 culture-proven cas es among organ transplant recipients. Four control patients were match ed to each case by age, sex, and date of admission. Cases and controls were compared with respect to past medical history and hospital expos ure variables. Odds ratios (ORs) and 95% confidence intervals (CIs) we re calculated for matched variables. Environmental culturing of air an d water supplies in and around the medical center was also performed. RESULTS: The case-control study revealed the following significant ris k factors for the acquisition of nosocomial Legionnaires` disease: imm unosuppressive therapy (OR = 32.7, CI = 4.5 to 302.6), nasogastric tub e use (OR = 18.4, CI = 2.6 to 166.2), bedbathing (OR = 10.7, CI = 2.2 to 59.0), and antibiotic therapy (OR = 14.6, CI = 2.9 to 84.4). Shower use (OR = 0.1, CI = 0 to 0.4) appeared to be a negative risk factor. Water cultures revealed Legionella pneumophila serogroup 1, monoclonal antibody subtype Philadelphia (identical to all patient isolates) in the ground-water supply to the hospital 1 hot-water tank, and 15% of 8 5 potable water sites tested. Air sampling of cooling towers, hospital air intakes, and medical air and oxygen supplies were negative for Le gionella organisms. CONCLUSIONS: This study confirms the importance of potable water in transmitting nosocomial Legionnaires' disease and su ggests that the organism gains access to the hospital via external wat er supplies. The risk factors identified in this case-control study pr ovide evidence that Legionnaires` disease may act as a superinfection in a nosocomial setting and is likely acquired by aspiration, similar to other nosocomial pneumonias.