Nosocomial Acinetobacter baumannii infections:: Microbiological and clinical epidemiology

Background: Acinetobacter baumannii is an important opportunistic pathogen that is rapidly evolving toward multidrug resistance and is involved in various nosocomial infections that are often severe. It is difficult to prevent A. baumannii infection because A. baumannii is ubiquitous and the epidemiology of the infections it causes is complex. Objective: To study the epidemiology of A. baumannii infections and assess the relation between fluoroquinolone use and the persistence of multidrug-resistant clones. Design: Three case-control studies and a retrospective cohort study. Setting: A 20-bed medical and surgical intensive care unit. Patients: Acinetobacter baumannii was isolated from 45 patients in urine (31%), the lower respiratory tract (26.7%), wounds (17.8%), blood (11.1%), skin (6.7%), cerebrospinal fluid (4.4%), and sinus specimens (2.2%). One death was due to A. baumannii infection. Measurements: Antimicrobial resistance pattern and molecular typing were used to characterize isolates. The incidence of A. baumannii infection and the use of fluoroquinolones were calculated annually. Results: Initially, 28 patients developed A. baumannii infection. Eleven isolates had the same antimicrobial susceptibility profile, genotypic profile, or both (epidemic cases), and 17 were heterogeneous (endemic cases). A surgical procedure done in an emergency operating room was the main risk factor for epidemic cases, whereas previous receipt of a fluoroquinolone was the only risk factor for endemic cases. The opening of a new operating room combined with the restriction of fluoroquinolone use contributed to a transitory reduction in the incidence of infection. When a third epidemiologic study was done, previous receipt of a fluoroquinolone was again an independent risk factor and a parallel was seen between the amount of intravenous fluoroquinolones prescribed and the incidence of endemic infection. Conclusion: Epidemic infections coexisted with endemic infections favored by the selection pressure of intravenous fluoroquinolones.