Multidrug-resistant Acinetobacter baumannii

Abstract

To understand the epidemiology of multidrug-resistant (MDR) Acinetobacter baumannii and define individual risk factors for multidrug resistance, we used epidemiologic methods, performed organism typing by pulsed-field gel electrophoresis (PFGE), and conducted a matched case-control retrospective study. We investigated 118 patients, on 27 wards in Israel, in whom MDR A. baumannii was isolated from clinical cultures. Each case-patient had a control without MDR A. baumannii and was matched for hospital length of stay, ward, and calendar time. The epidemiologic investigation found small clusters of up to 6 patients each with no common identified source. Ten different PFGE clones were found, of which 2 dominated. The PFGE pattern differed within temporospatial clusters, and antimicrobial drug susceptibility patterns varied within and between clones. Multivariate analysis identified the following significant risk factors: male sex, cardiovascular disease, having undergone mechanical ventilation, and having been treated with antimicrobial drugs (particularly metronidazole). Penicillins were protective. The complex epidemiology may explain why the emergence of MDR A. baumannii is difficult to control.

Figure 1

Distribution of case-patients according to ward.

Figure 2

Monthly case distribution

Figure 3

A typical pulsed-field gel electrophoresis analysis of selected isolates of A. baumannii restricted with ApaI. Lane 1 shows λ ladder used as molecular size marker. Lanes 11–13 are of strains not included in the trial. The gel shows 6 different clones of A. baumannii: 5 isolates belong to clone A and that 2 belong to clone B (the two dominant clones). Single isolates belonging to clones C, D, E, and F can be seen.