1. a School of Medicine, University of California , San Francisco , USA
2. b Wits Reproductive Health & HIV Institute, University of the Witswatersrand , Johannesburg , South Africa
3. c Faculty of Psychology , Università di Trieste , Trieste , Italy
4. d Centre for Public Health Research, Kenya Medical Research Institute (KEMRI) , Nairobi , Kenya
5. e Centre for Microbiology Research, Kenya Medical Research Institute (KEMRI) , Nairobi , Kenya
6. f School of Public Health, University of Alabama at Birmingham , Birmingham , Alabama , USA