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

ABSTRACT 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.