NOSOCOMIAL OUTBREAK CAUSED BY A MULTIRESISTANT CLONE OF ACINETOBACTER-BAUMANNII - RESULTS OF THE CASE-CONTROL AND MOLECULAR EPIDEMIOLOGIC INVESTIGATIONS

OBJECTIVE: To describe a nosocomial outbreak caused by multiresistant Acinetobacter baumannii. DESIGN: Descriptive and case-control study. A ntibiotic susceptibilities and pulsed-field gel electrophoresis (PFGE) of genomic DNA digested with SfiI and also with ApaI were used as mar kers of strain identity. SETTING: A large medical school-affiliated ho spital in the city of Houston, Texas. RESULTS: During a 10-week period , A baumannii was isolated from 25 patients admitted to the intensive care unit (ICU). The attack rate was 14.3 per 100 ICU admissions. Case patients were intubated more frequently and for longer periods, and h ad longer ICU and hospital stays (P<0.05 for each of these characteris tics). Multivariate logistic regression analysis identified the length of ICU stay and the use of third-generation cephalosporins as associa ted with the acquisition of A baumannii. Patients infected with A baum annii had a higher mortality rate than colonized patients and control patients (P<0.01). Sixteen isolates recovered from these 25 patients w ere susceptible only to imipenem/cilastatin, and PFGE confirmed that a single clone was the cause of this outbreak. Nine isolates of A bauma nnii from patients infected or colonized in two other hospitals in Hou ston during the same period, differed from the outbreak isolates by th eir susceptibility to ciprofloxcin. However, PFGE results were identic al, indicating unsuspected genetic relatedness among isolates from thr ee different hospitals. CONCLUSIONS: A baumannii is an important nosoc omial opportunistic pathogen and can adversely affect the outcome of I CU patients who acquire this organism. This outbreak was caused by a s ingle clone that was isolated concurrently from three hospitals.