Trends in HIV -1 Incidence in a Cohort of Prostitutes in Kenya: Implications for HIV -1 Vaccine Efficacy Trials
Ngugi, Elizabeth N
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Background: Accurate predictions of HIV-I incidence in potential study populations are essential for designing HIV-I vaccine efficacy trials. Lillie information is available on the estimated incidence of HIV-I in such populations. especially information on incidence over time and incidence while participating in risk-reduction programs. Objectives: To examine time trends in HIV-I incidence in a vaccine preparedness cohort. Design: Prospective cohort study of female prostitutes in Momhasn, Kenya. Methods: HIV -I incidence was determined using open and closed coll.".1 desig'''. Generalized estimating equations were used to model HIV -I und sexually trunsmittcd disease (STD) incidence and sexual risk behaviors over time. Results: When analyzed as a closed cohort, HIV-I incidence dcclincdjlO-l"old during 3 years of follow-up (from 17.4 to 1.7 cases/I 00 person-years: I' < .OOr). More than 50% of the cases of mV-1 occurred during the first 6 months after enrollment. and 73% during the first 12 months. When analyzed as an open whorl. lilY -I incidence density fell during the first 4 calendar years, influenced hy accumulation of lower risk participants and variations in study recruitment. Si!,!nilil';rnt declines occurred in both STD incidence and high-risk sexual behaviors during follow-up. Conclusions: This study documents a dramatic decline in the risk of IllY-I infection while participating in a prospective cohort, with most seroconvcrsions occurring within I year of enrollment. Variations in HIV-I incidence within high-risk populations should be anticipated during the design of vaccine trials.