Birgitta Versluijs

113 Respiratory virus infection pre-HCT and alloimmune-mediated lung syndromes than 0.7, FEV1 of less than 75%, and evidence of air-trapping (on PFTs or HRCT scans) in the absence of respiratory tract infection. 10 We adjusted these definitions by not exclu- ding patients only for a longer existing positive PCR result for RVs when they fulfilled all other criteria for allo-LSs, as described previously. 6 Additionally, we investigated the association between allo-LSs and overall survival, tre- atment-related mortality (TRM), and aGVHD and chronic GVHD in other organs — classification according to the Glucksberg criteria. 11 Statistical analysis The duration of follow-up was the time to development of allo-LSs or death or the last assessment for survivors. We assessed the association between outcome and patient-re- lated variables (age at transplantation, sex, RV status, RV viral load expressed as Ct value, and cytomegalovirus status), disease (malignancy, bone marrow failure syndromes, and inborn errors of metabolism and primary immune deficiency), conditioning regimen (chemotherapy or total-body irradiation based), and donor factors (stem cell source and HLA disparity). Because of sample size, the median Ct value (as semiquantitative viral load) was taken to dichotomize the group in high or low RV viral load. Variables associated with a P value of less than .1 by using univariate analysis were selec- ted for multivariate analysis. Probabilities of event-free and overall survival were calcula- ted by using the Kaplan-Meier estimate; we used the 2-sided log-rank test for univariate comparisons. Time-dependent outcomes were analyzed by using Cox proportional ha- zard models. For the end points of allo-LSs, overall survival, and TRM, we used Fine- Gray competing risk regressions. For dichotomous variables, univariate and multivariate logistic regression analyses were done. All statistical analyses were performed with either SPSS 22 (SPSS, Chicago, Ill) or R, version 3.0.1, software. Results Patients' characteristics A total of 273 patients underwent transplantation during the study period. One hundred seventy-nine patients had paired NPA and BAL samples before HCT available for analy- sis; they were evaluated in the study. The other 94 patients did not have NPAs and BAL fluid taken. The median age at transplantation was 6.8 years (range, 0.6-22.7 years); half of the patients underwent transplantation for a malignant disease, and CB (54%) was the main source of stem cells, followed by bone marrow (44%). Baseline characteristics are shown in Table I. Median follow-up of surviving patients was 4.3 years (range, 0.7-9.7 years). 7