Colonisation by multidrug-resistant organisms in health workers in primary care: narrow spectrum oral antimicrobials are a risk factor

Background: Limited information exists on carriage of multidrug-resistant organisms (MDRO) by health workers (HWs) in primary care settings. This study aims to determine the prevalence of MDRO carriage among HWs in primary care and to identify associated risk factors. Methods: A cross-sectional study was conducted across all 12 primary care units in São Caetano do Sul-SP, Brazil, from October to December 2023. Self-collected samples (nasal, oropharyngeal, and inguinal) were obtained. Environment cultures (potable water, sewage and stream water) were evaluated. Stenotrophomonas maltophilia isolates (human and environmental) were typed. Results: The study included 265/288 (92%) of HWs in primary care teams, mostly women with a median age of 47 years (IQR 38—57); 78% had no comorbidities. MDRO colonisation was found in 8.7% (23 HWs). The following bacteria were found: S. maltophilia (n = 9; 3.4%) in inguinal swabs; methicillin-resistant Staphylococcus aureus (n = 8; 3%) from all sites; extended-spectrum ß-lactamase-producing bacteria (n = 5; 2%) in inguinal swabs; and vancomycin-resistant enterococci in an inguinal swab (n = 1; 0.4%). Previous antibiotic use was significantly associated with MDRO colonisation (OR 2.91, 95% CI 1.19–7.09, p = 0.018), mainly narrow spectrum oral beta-lactams and macrolides. S. malthophilia was polyclonal and human and environmental isolates differed. Conclusion: Colonisation by MRSA, VRE, and ESBL-producing bacteria was low; however, 4% were surprisingly colonized by polyclonal S. maltophilia. This pathogen may also suggest using narrow-spectrum rather than the expected broad-spectrum antimicrobials. Antibiotic use was the only risk factor found, mainly with oral narrow-spectrum drugs.