1. Fundació Sida i Societat, Barcelona, Spain
2. PhD Programme in Public Health and Methodology of Biomedical Research, Department of Paediatrics, Obstetrics and Gynaecology, and Preventive Medicine, Universitat Autònoma de Barcelona, Bellaterra 08193, Barcelona, Spain
3. CIBER Epidemiología y Salud Pública, (CIBERESP), Spain
4. Fundació Sida i Societat, Escuintla, Guatemala
5. Center for Epidemiological Studies on HIV/AIDS and STI of Catalonia (CEEISCAT), ICO/Health Department, Badalona, Spain
6. Clinical Laboratory of Primary Health Bon Pastor, Barcelona, Spain
7. Primary Health Care Centre, Escuintla, Guatemala