RecruitingProcedureThe Longitudinal Impact of Respiratory Viruses on Bronchiolitis Obliterans Syndrome After Allogeneic Hematopoietic Cell Transplantation (The RV-BOS Study)This observational trial studies whether respiratory viruses are the cause of lung disease (bronchiolitis obliterans syndrome \[BOS\] or graft-versus-host disease of the lung) and changes in lung function in patients who have received a donor stem cell transplant. Patients with chronic graft-versus-host disease (cGVHD) are at higher risk of developing BOS. Studies have also shown that patients who had a respiratory viral illness early after their transplant are at higher risk of developing lung problems later on. Patients who are at risk and who already have BOS might benefit from being monitored more closely. Spirometry is a way of assessing a patient's lung function and is often used to diagnose lung disease. Spirometry measured at home with a simple handheld device may reduce the burden of performing pulmonary function testing at a facility and potentially help patients get their lung disease diagnosed and treated sooner.