Characterizing Respiratory Virus Infections during the Peri-engraftment Period of Allogeneic Hematopoietic Cell Transplant.

Background: Community-acquired respiratory virus (CARV) infections are frequent and potentially severe in allogeneic hematopoietic stem cell transplant (allo-HCT) recipients. However, their impact during the peri-engraftment period remains underexplored.

Methods: In this retrospective multicenter study, we assessed the characteristics, effects on neutrophil engraftment, and risk factors for lower respiratory tract disease (LRTD) progression and 100-day mortality of symptomatic peri-engraftment CARV infections [from Day -8 until Day +36 after stem cell infusion]. A total of 112 allo-HCT recipients and 114 CARV episodes were included. Univariable and multivariable Cox regression analyses and cumulative incidence estimates were used.

Results: The median patient age was 51 years. Rhinovirus (47%) and respiratory syncytial virus (23%) were the most common pathogens. Half of the infections occurred before neutrophil engraftment (median day +18), and 50% progressed to LRTD. The 100-day mortality rate was 17%, increasing to 27% in those with LRTD. CARV infection prior to engraftment was associated with delayed neutrophil recovery (Day +18 vs. +16; p = 0.04) in multivariable cause-specific Cox regression analysis (HR 0.42, p < 0.001). Multivariable analysis identified lymphocyte count <0.2×10⁹/L (HR 3.1, p = 0.004) and active graft-versus-host disease (HR 2.36, p = 0.004) as independent predictors of LRTD. Risk factors for 100-day mortality included LRTD (HR 3.34, p = 0.04), use of anti-thymocyte globulin (HR 3.48, p = 0.019), and bacterial coinfection (HR 4.48, p = 0.006).

Conclusion: CARV infections during the peri-engraftment allo-HCT phase carry a high risk for delayed engraftment and LRTD in case of profound lymphopenia and GvHD. LRTD, ATG use, and bacterial coinfections contributed significantly to mortality.