Trends in HIV-1 incidence in a cohort of prostitutes in Kenya: implications for HIV-1 vaccine efficacy trials.
BACKGROUND
Accurate predictions of HIV-1 incidence in potential study populations are essential for designing HIV-1 vaccine efficacy trials. Little information is available on the estimated incidence of HIV-1 in such populations, especially information on incidence over time and incidence while participating in risk-reduction programs.


OBJECTIVE
To examine time trends in HIV-1 incidence in a vaccine preparedness cohort.


METHODS
Prospective cohort study of female prostitutes in Mombasa, Kenya.


METHODS
HIV-1 incidence was determined using open and closed cohort designs. Generalized estimating equations were used to model HIV-1 and sexually transmitted disease (STD) incidence and sexual risk behaviors over time.


RESULTS
When analyzed as a closed cohort, HIV-1 incidence declined 10-fold during 3 years of follow-up (from 17.4 to 1.7 cases/100 person-years; p <.001). More than 50% of the cases of HIV-1 occurred during the first 6 months after enrollment, and 73% during the first 12 months. When analyzed as an open cohort, HIV-1 incidence density fell during the first 4 calendar years, influenced by accumulation of lower risk participants and variations in study recruitment. Significant 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 HIV-1 infection while participating in a prospective cohort, with most seroconversions occurring within 1 year of enrollment. Variations in HIV-1 incidence within high-risk populations should be anticipated during the design of vaccine trials.
Baeten
J M
JM
Departments of Epidemiology, Biostatistics, and Medicine, University of Washington, Seattle, Washington, USA. jbaeten@u.washington.edu
Richardson
B A
BA
Martin
H L
HL
Nyange
P M
PM
Lavreys
L
L
Ngugi
E N
EN
Mandaliya
K
K
Ndinya-Achola
J O
JO
Bwayo
J J
JJ
Kreiss
J K
JK
D016915:AIDS Vaccines; D000293:Adolescent; D000328:Adult; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D015658:HIV Infections / Q000453:epidemiology* / Q000517:prevention & control; D015497:HIV-1 / Q000276:immunology; D006801:Humans; D015994:Incidence; D007630:Kenya / Q000453:epidemiology; D008875:Middle Aged; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D011477:Sex Work / Q000706:statistics & numerical data*; D012725:Sexual Behavior; D012749:Sexually Transmitted Diseases / Q000453:epidemiology
D016915:AIDS Vaccines