An Outbreak of Serratia marcescens in a Cardiothoracic Surgery Unit Associated with an Infected Solution of Pre-Prepared Syringes

<b>Background/Objectives:</b> The aim of the present study is to report an outbreak of bloodstream infections caused by <i>Serratia marcescens</i> in patients undergoing postoperational procedures in the Cardiothoracic Department and to describe the epidemiological investigations and control measures undertaken. A cluster of bacteremia due to <i>Serratia marcescens</i> was identified in blood cultures from postoperative patients in the Cardiothoracic Surgery Department in November 2023. <b>Methods:</b> Active surveillance by the hospital's prevention and control team was initiated. Interviews with nurses and sanitary personnel and reviews of the most common procedures, such as hand washing, bladder catheterization, and intravenous catheter care, were performed. Culturing samples from hospital personnel, postoperative patients, and the environment, including pressure transducers, tap water, soap, therapeutic solutions, antiseptics, respirators, and various intravenous preparations, were drawn up. Overall, 225 samples were collected, including 149 blood cultures, and these were all sent to the Hospital's Microbiology Laboratory. <b>Results:</b> Twenty-three out of forty-seven postoperative patients had positive blood cultures for <i>Serratia marcescens.</i> All the postoperative patients involved in the outbreak received cefepime according to antimicrobial susceptibility testing. Three pre-prepared flushing syringes were found to be positive for <i>Serratia marcescens</i> as well. The Cardiothoracic Department was kept under surveillance with hand hygiene measures, infusion preparation, medical device use, and cleaning procedures reviewed by the infection's prevention and control team. <b>Conclusions:</b> Undoubtedly, nosocomial outbreaks represent an important health issue regarding morbidity, mortality, and costs. Timely interventions by the hospital's infection prevention and control team may be life-saving under these circumstances.