1. Department of Medicine, Queen Elizabeth Hospital, Hong Kong, China.
2. Infectious Diseases Service, Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, USA.
3. Pediatric Bone Marrow Transplantation Service, Department of Pediatrics, Memorial Sloan Kettering Cancer Center, New York, USA.
4. Weill Cornell Medical College, Cornell University, New York, USA.