From Colonisation to Infection: Assessing the BSI Potential in Patients with KPC, NDM, VRE and CRAB Rectal Colonisation

Introduction: Multi-drug-resistant organisms (MDROs) that mostly contribute to nosocomial infections include carbapenem-resistant Enterobacterales that produce Klebsiella pneumoniae carbapenemase (KPC) and New Delhi metallo-β-lactamase (NDM), carbapenem-resistant Acinetobacter baumannii (CRAB) and vancomycin-resistant Enterococcus faecium (VRE). Patients colonised by these MDROs are at high risk for developing bloodstream infections (BSIs) by the same pathogen, emphasising the need for surveillance and intervention. Methods: This retrospective study included patients admitted to medical, surgical, and intensive care unit (ICU) wards in the IRCCS Policlinico San Matteo (Pavia, Italy) between January 2019 and October 2024 with rectal colonisation by KPC, NDM, VRE and CRAB. Demographic, clinical and microbiological data were extracted from electronic records. Logistic regression with stepwise model-building identified risk factors for BSI development. Results: A total of 1969 patients colonised with MDRO were identified: 79% of them were colonised by KPC, VRE, CRAB or NDM. Among the 1960 hospitalisations involving these specific rectal colonisations, the overall rate of BSIs was 9.4%, with CRAB and KPC showing the highest rates (20.0% and 12.6%, respectively). ICU hospitalisation was significantly associated with an increased risk of BSI in patients colonised with KPC, NDM and VRE. Haematological malignancies and bone marrow transplantation were independent risk factors for BSI in patients colonised with KPC (odds ratio [OR] = 3.22, p = 0.037) and VRE (OR = 4.07, p = 0.004) whereas solid organ transplantation increased BSI risk among patients colonised with CRAB (OR = 11.83, p = 0.034). Conclusions: Our findings show heterogeneous BSI risk among MDROs, with CRAB and KPC being the most dangerous, especially in patients in the ICU, followed by VRE in onco-haematological cases. These results support developing prevention strategies for critically ill and immunocompromised patients.