Background: Hospital environments, particularly shared rooms, are vulnerable to the transmission of carbapenem-resistant Enterobacterales (CRE). The incidence of CRE colonization in the Korean homeless population remains unknown. This study aimed to analyze the impact of targeted active surveillance of CRE in hospital wards following two outbreaks.
Methods: This retrospective study was conducted in a homeless ward with shared rooms at a municipal hospital in Seoul. The CRE incidence was calculated from October 1, 2023, to May 31, 2024. Active surveillance was initiated on January 22, 2024. Poisson regression analysis was used to compare CRE incidence events at three months before and four months after the intervention. The risk factors for CRE colonization were also analyzed.
Results: The CRE colonization rate decreased from 1.149 to 0.815 per 1,000 patient-days post-intervention; however, the change was not statistically significant (rate ratio: 0.986, 95% confidence interval (95% CI): 0.389-2.496, P=0.976). In contrast to the secondary cases, one acquired CRE case was detected after the intervention without an outbreak. The CRE colonization rate was higher in the homeless ward than in the general ward. CRE colonization was significantly associated with age (adjusted odds ratio (aOR), 1.071; 95% CI: 1.014-1.132; P=0.014), previous antibiotic exposure (aOR, 6.796; 95% CI: 1.215-38.029; P=0.029), and co-colonization with other multidrug resistant bacteria (aOR, 7.168; 95% CI: 2.224-23.096; P=0.001).
Conclusion: A relatively high incidence of CRE colonization was observed in the homeless ward. After active surveillance, no CRE outbreaks occurred following the implementation.

Keywords: Multiple drug resistance, Pathogen transmission, Infection control, Homeless Mward, Resource-limited settings