1. Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, USA;
2. Department of Biostatistics, Yale School of Public Health, New Haven, Connecticut, USA;
3. Center for Interdisciplinary Research on AIDS, Yale University, New Haven, Connecticut, USA;
4. Department of Chronic Disease Epidemiology, Yale School of Public Health, New Haven, Connecticut, USA