Prevalence of and Risk Factors for Multidrug-Resistant Acinetobacter baumannii Colonization Among High-Risk Nursing Home Residents

OBJECTIVE. To characterize the epidemiology of multidrug-resistant (MDR) Acinetobacter baumannii colonization in high-risk nursing home (NH) residents. DESIGN. Nested case-control study within a multicenter prospective intervention trial. setting. Four NHs in Southeast Michigan. PARTICIPANTS. Case patients and control subjects were NH residents with an indwelling device (urinary catheter and/or feeding tube) selected from the control arm of the Targeted Infection Prevention study. Cases were residents colonized with MDR (resistant to >= 3 classes of antibiotics) A. baumannii; controls were never colonized with MDR A. baumannii. METHODS. For active surveillance cultures, specimens from the nares, oropharynx, groin, perianal area, wounds, and device insertion site(s) were collected upon study enrollment, day 14, and monthly thereafter. A. baumannii strains and their susceptibilities were identified using standard microbiologic methods. RESULTS. Of 168 NH residents, 25 (15%) were colonized with MDR A. baumannii. Compared with the 143 controls, cases were more functionally disabled (Physical Self-Maintenance Score >24; odds ratio, 5.1 [95% CI, 1.8-14.9]; P<.004), colonized with Proteus mirabilis (5.8 [1.9-17.9]; P<.003), and diabetic (3.4 [1.2-9.9]; P<.03). Most cases (22 [88%]) were colonized with multiple antibiotic-resistant organisms and 16 (64%) exhibited co-colonization with at least one other resistant gram-negative bacteria. CONCLUSION. Functional disability, P. mirabilis colonization, and diabetes mellitus are important risk factors for colonization with MDR A. baumannii in high-risk NH residents. A. baumannii exhibits widespread antibiotic resistance and a preference to colonize with other antibiotic-resistant organisms, meriting enhanced attention and improved infection control practices in these residents.