1. Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA
2. School of Public Health and Health Sciences, University of Massachusetts, Amherst, Massachusetts, USA
3. Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
4. Rakai Health Sciences Program, Kalisizo, Uganda
5. Department of Biostatistics, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA
6. Department of Health, Behavior and Society, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA