Prevalence of multidrug-resistant organisms and risk factors for carriage in long-term care facilities: A nested case-control study

Background: Long-term care facilities (LTCFs) are a potentially important reservoir of multidrug-resistant (MDR) organisms; however, limited data exist. Methods: A point-prevalence study was conducted in four co-located LTCFs in Australia. Nasal and rectal swabs were cultured for methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and MDR Gram-negative bacilli (GNB). Molecular typing and resistance detection were performed. Risk factors for colonization with an MDR organism were determined using a nested case-control study. Results: Consent was obtained from 115 (85 ) of 136 eligible participants. Forty-one (36 ) residents carried at least one type of MDR organism. The prevalence was 16 MRSA (n=18), 6 VRE (n=7) and 21 MDR GNB [n=24; including extended-spectrum b-lactamase (ESBL)-producing Escherichia coli (n=12) and Acinetobacter baumannii (n=6)]. The majority of ESBL-producing E. coli and A. baumannii were clonal. Current wound management [adjusted OR (AOR) 8.81 (95 CI 2.78-27.94), P <0.001], medical device in situ [AOR 5.58 (95 CI 1.34-23.32), P=0.018] and pressure ulcer [AOR 3.69 (95 CI 1.06-12.86), P=0.04] were independent risk factors for MDR organism colonization. Advanced dementia [AOR 3.54 (95 CI 1.23-10.23), P=0.02] and prolonged antibiotic use [AOR 2.95 (95 CI 1.01-8.60), P=0.047] were independently associated with MRSA colonization, whilst current wound management [AOR 15.59 (95 CI 4.85-50.10), P <0.001] and fluoroquinolone use [AOR 4.27 (95 CI 1.20-15.25), P=0.025] were risk factors for MDR GNB colonization. Conclusions: LTCFs are an important reservoir of MDR organisms, with person-to-person transmissions being a potential issue. We have identified several predictors of colonization with MDR organisms, allowing a more targeted management of high-risk residents.