Clinical Outcomes of Low‐Grade Cytomegalovirus DNAemia in Hematopoietic Stem Cell Transplantation Recipients Receiving Letermovir Prophylaxis

Cytomegalovirus (CMV) infection remains a major contributor to CMV-related and hematologic adverse outcomes in hematopoietic stem cell transplantation (HSCT) recipients. While letermovir has improved CMV prophylaxis strategies in this population, the clinical implications of low-grade CMV DNAemia during letermovir prophylaxis remain uncertain. We retrospectively analyzed 255 HSCT recipients who received letermovir at a tertiary hospital in Korea. Patients were stratified into three groups based on the highest CMV DNAemia levels observed during letermovir prophylaxis: no DNAemia (n = 72), low-grade DNAemia (< 1000 IU/mL; n = 171), and high-grade DNAemia (≥ 1000 IU/mL; n = 12). The association between low-grade CMV DNAemia and clinical outcomes was assessed using a multivariate Cox proportional hazards model. Most low-grade DNAemia cases were transient and resolved without antiviral therapy. Compared to no DNAemia, low-grade CMV DNAemia was not associated with an increased risk of clinically significant CMV infection by Day 100 (p = 0.262) or Day 365 (p = 0.399). No significant associations were observed with engraftment failure (p = 0.098), disease relapse (p = 0.165), or all-cause mortality (p = 0.537). Our findings suggest that close monitoring may be sufficient for low-grade DNAemia under letermovir prophylaxis.