1. Department of Respiratory and Critical Care Medicine, Singapore General Hospital, Singapore 169608, Singapore
2. Duke-NUS Graduate Medical School, Singapore 169857, Singapore
3. Lee Kong Chian School of Medicine, Nanyang Technological University, Clinical Sciences Building, 11 Mandalay Road, Singapore 308232, Singapore
4. Department of Respiratory and Critical Care Medicine, Tan Tock Seng Hospital, Singapore 308433, Singapore