title: Nosocomial Legionnaires' disease: aspiration as a primary mode of disease acquisition.
abstract: OBJECTIVE
  Nosocomial Legionnaires' disease remains a significant problem with many unresolved questions regarding transmission of legionella organisms to patients. We performed a case-control and environmental study to identify risk factors and modes of transmission of Legionella infection during an outbreak of nosocomial Legionnaires' disease in a military medical center.
  
  
  METHODS
  During the calendar year 1989, 14 cases of nosocomial Legionnaires' disease were identified by active surveillance following the discovery of 2 culture-proven cases among organ transplant recipients. Four control patients were matched to each case by age, sex, and date of admission. Cases and controls were compared with respect to past medical history and hospital exposure variables. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated for matched variables. Environmental culturing of air and water supplies in and around the medical center was also performed.
  
  
  RESULTS
  The case-control study revealed the following significant risk factors for the acquisition of nosocomial Legionnaires' disease: immunosuppressive therapy (OR = 32.7, CI = 4.5 to 302.6), nasogastric tube 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 85 potable water sites tested. Air sampling of cooling towers, hospital air intakes, and medical air and oxygen supplies were negative for Legionella organisms.
  
  
  CONCLUSIONS
  This study confirms the importance of potable water in transmitting nosocomial Legionnaires' disease and suggests that the organism gains access to the hospital via external water supplies. The risk factors identified in this case-control study provide evidence that Legionnaires' disease may act as a superinfection in a nosocomial setting and is likely acquired by aspiration, similar to other nosocomial pneumonias.
authors.affiliation: Department of Infectious Disease, Wilford Hall USAF Medical Center, Lackland Air Force Base, Texas 78236-5300.
authors.forename: S P
authors.initials: SP
authors.lastname: Blatt
authors.forename: M D
authors.initials: MD
authors.lastname: Parkinson
authors.forename: E
authors.initials: E
authors.lastname: Pace
authors.forename: P
authors.initials: P
authors.lastname: Hoffman
authors.forename: D
authors.initials: D
authors.lastname: Dolan
authors.forename: P
authors.initials: P
authors.lastname: Lauderdale
authors.forename: R A
authors.initials: RA
authors.lastname: Zajac
authors.forename: G P
authors.initials: GP
authors.lastname: Melcher
mesh_terms: D000328:Adult; D000368:Aged; D000391:Air Microbiology; D016022:Case-Control Studies; D003428:Cross Infection / Q000453:epidemiology / Q000635:transmission*; D004196:Disease Outbreaks; D005260:Female; D006772:Hospitals, Military; D006801:Humans; D001239:Inhalation; D016952:Legionella pneumophila / Q000302:isolation & purification; D007877:Legionnaires' Disease / Q000453:epidemiology / Q000635:transmission*; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D012307:Risk Factors; D013781:Texas / Q000453:epidemiology; D014871:Water Microbiology