The authors thank the study volunteers and nongovernmental organization leaders who understood the social importance of participating in this scientific effort, notwithstanding difficulties. We also acknowledge the support provided by the staff of Centro de Pesquisa Hospital Evandro Chagas (CPqHEC/FIOCRUZ) and the National Reference Centre of Viral Hepatitis (IOC/FIOCRUZ), which made it possible to execute this study. Financial support was provided by the National STD/AIDS Program of the Brazilian Ministry of Health, World Health Organization Global Program on AIDS, Joint United Nations Program on AIDS, Brazilian National Research Council (CNPq), and the Oswaldo Cruz Foundation (FIOCRUZ). The staff members of Projeto Rio include Frits Sutmaller (Coordinator), Claudia Teresa Vieira de Souza, Amilton Xavier, Jr, Helena Santos Martins, Dionne Peluso de Oliveira Costa, Paulo Starling BrandÃo Junior, and Therezinha Lucy Penna.