Serratia marcescens Infections from Inhalation Therapy Medications: Nosocomial Outbreak

An outbreak of nosocomial infections caused by non-pigmented Serratia marcescens is described. There were 655 bacterial isolates from 374 patients during a 10-month period; 50.4% of isolates were from sputum, 24.5% from urine, and the remainder from wounds, blood, and miscellaneous sites. Opened bottles of aerosol inhalation therapy medications were implicated. Forty-three percent of a random sample of opened bottles were contaminated with S. marcescens, and viable bacterial counts reached 107 organisms per milliliter. Factors responsible for initiation of the epidemic were defined, control measures were instituted, and the outbreak stopped. This experience emphasizes the problems in recognition of hospital-associated infections. The importance of underlying host determinants in the occurrence of disease from exposure to Gram-negative bacilli is discussed.