[1] Ctr Dis Control & Prevent, Resp & Enter Virus Branch, Natl Ctr Infect Dis, Atlanta, GA 30333 USA
[2] Clin Trials & Surveys, Baltimore, MD USA
[3] NICHHD, Pediat Adolescent & Maternal AIDS Branch, Bethesda, MD 20892 USA
[4] Baylor Coll Med, Houston, TX 77030 USA