Respiratory viral infections occurring after hematopoietic stem cell transplantation.

Respiratory viral infection is one of the most crucial complications after hematopoietic stem cell transplantation (HSCT), which affects approximately 60% of HSCT recipients within one year after transplantation. Prevalence of progression from upper respiratory tract infection to lower respiratory tract disease (LRD) among HSCT recipients is 15-20% and day-90 mortality after LRD is as high as 40%. Risk factors for the progression to LRD are early infection after HSCT, low neutrophil or lymphocyte count, old age, and corticosteroid use. Aerosolized or oral ribavirin for respiratory syncytial virus infection and neuraminidase inhibitors for influenza are effective for the prevention of progression to LRD and mortality from LRD. Conversely, there are no definitive data concerning the efficacy of intravenous immunoglobulin. In cases of respiratory viral infection after HSCT, we recommend reduction of steroid dosage to less than 1 mg/kg/day, if applicable. Future directions for the management of respiratory viral infections in Japan are widespread availability of multiplex PCR testing and the introduction of new antiviral drugs.