1. University of Sao Paulo, Ribeirão Preto, Sao Paulo, Brazil
2. Westat, Rockville, Maryland
3. Federal University of Minas Gerais, Belo Horizonte, Brazil
4. Hospital dos Servidores do Estado, Rio de Janeiro, Brazil
5. Hospital General de Agudos Jose Maria Ramos Mejia, Buenos Aires, Argentina
6. Pediatric, Adolescent, and Maternal AIDS Branch, Center for Research for Mothers and Children, National Institute of Child Health and Human Development, Bethesda, Maryland