1. Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA
2. Macha Research Trust, Choma, Zambia
3. Department of International Health, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA
4. Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
5. Virology Laboratory, University Teaching Hospital, Lusaka, Zambia
6. Department of Microbiology and Immunology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD, USA