1. Program in Emerging Infectious Diseases, Duke–National University of Singapore, Singapore, Singapore.
2. Department of Pathology, Duke University Medical Center, Durham, NC 27705, USA.
3. Department of Microbiology and Immunology, National University of Singapore, Singapore, Singapore.
4. Saw Swee Hock School of Public Health, National University of Singapore, Singapore, Singapore.
5. Department of Infectious Diseases, Singapore General Hospital, Singapore, Singapore.