Grace John is an internist/pediatrician, currently a fellow in Infectious Diseases/Epidemiology at the University of Washington. During the past 2 years, she has been a lead research field investigator with the Breastfeeding Transmission of HIV Study in Nairobi, Kenya. Dr. John began to study the area of genital tract shedding of HIV-1 during pregnancy for her MPH thesis and would like to further study this topic in the context of perinatal transmission in the Breastfeeding Study cohort. The statistical and epidemiologic component of the project presents new approaches for the investigator and mentored training in these areas will broaden her capabilities as an epidemiologic investigator. The project she proposes has potential for further development, specifically in the evaluation of the effect of topical microbicide interventions on perinatal transmission, and will provide experience that will enable her to pursue her long-term goal of an academic career with a research focus on perinatal epidemiology of infectious diseases, specifically HIV-1. Intrapartum transmission of HIV-1 may account for the majority of infection in nonbreastfeeding infants. The effect of genital viral burden on transmission is unknown. The aim of this project is to determine the prevalence, quantity, and correlates of cervical and vaginal HIV-1 DNA and RNA in 250 HIV-1 infected women at 32 weeks gestation. In order to determine the temporal pattern of genital shedding of HIV-1 during and after pregnancy a subset of 50 women will be evaluated at three antenatal and 2 postnatal examinations. The second part of the project will determine the effect of antenatal genital tract shedding of HIV-1 on intrapartum transmission by utilizing information from the cohort on infant infection status at 6 weeks of age. An understanding of this relationship is important for designing rational interventions to prevent vertical transmission of HIV-1.