1. Bristol Medical School, University of Bristol, Bristol, United Kingdom;
2. National Institute of Health Research (NIHR) Health Protection Research Unit (HPRU) in Evaluation of Interventions, Bristol, United Kingdom;
3. Pakistan Medical Research Council (PMRC), Islamabad, Pakistan;
4. Department of Medicine, Aga Khan University, Karachi, Pakistan;
5. National AIDS Control Programme, Islamabad, Pakistan;
6. Centers for Disease Control and Prevention, Atlanta, Georgia