Endemic Serratia marcescens in the Veterans Administration Hospital in Pittsburgh, Pa., 1971--1976.

The incidence of infections due to Serratia marcescens increased steadily at the Veterans Administration Hospital in Pittsburgh, Pennsylvania from 1970 to mid 1975 followed by a decline extending into 1977. One hundred eighty-four Serratia marcescens isolates were collected from 123 patients over a 4-month period in 1975 and were characterized by stereotype and antibiotic sensitivity. Three-fourths of the isolates were clinically significant. Among 24 stereotypes O-:H2 predominated in the urinary tract and O-H12 in respiratory secretions. Clusters of serotypes were on occasion identified in the GU Surgery Ward and the Intensive Care Unit. Uninary isolates showed remarkable resistance to antibiotics; only two thirds were susceptible to amikacin, the most effective agent in vitro. The patients from whom Serratia was isolated were older than the general hospital population (60 vs. 53.6 years of age), were hospitalized longer than the age-corrected controls (62 vs. 34.5 days) and two-thirds of thirds of them acquired the infection in the hospital. Uninary catheterization and prior antibiotic therapy were significant risk factors for urinary infections, and prior surgery contributed to recovery of Serratia from the respiratory tract. Serotype and antibiotype differences between isolates from the urinary and those from the respiratory tract suggest that strains evolved a site specificity.