title: Reduced rates of HIV acquisition during unprotected sex by Kenyan female sex workers predating population declines in HIV prevalence.
abstract: OBJECTIVE
  Female sex workers (FSWs) form a core group at high risk of both sexual HIV acquisition and secondary transmission. The magnitude of these risks may vary by sexual risk taking, partner HIV prevalence, host immune factors and genital co-infections. We examined temporal trends in HIV prevalence and per-act incidence, adjusted for behavioral and other variables, in FSWs from Nairobi, Kenya.
  
  
  METHODS
  An open cohort of FSWs followed since 1985. Behavioral and clinical data were collected six monthly from 1985 to 2005, and sexually transmitted infection (STI) diagnostics and HIV serology performed. A Cox proportional hazards model with time-dependent covariables was used to estimate infection risk as a function of calendar time.
  
  
  RESULTS
  HIV prevalence in new FSW enrollees peaked at 81% in 1986, and was consistently below 50% after 1997. Initially uninfected FSWs remained at high risk of acquiring HIV throughout the study period, but the rate of HIV acquisition during unprotected sex with a casual client declined by over four-fold. This reduction correlated closely with decreases in gonorrhea prevalence, and predated reductions in the Kenyan HIV population prevalence by over a decade.
  
  
  CONCLUSIONS
  The per-act rate of HIV acquisition in high-risk Nairobi FSWs fell dramatically between 1985 and 2005. This decline may represent the impact of improved STI prevention/therapy, immunogenetic shifts in at-risk women, or changes in the proportion of HIV exposures occurring with clients who had acute HIV infection. Declining HIV incidence in high-risk cohorts may predict and/or be causally related to future reductions in population prevalence.
authors: Department of Medical Microbiology, University of Nairobi, Nairobi, Kenya.
authors: Joshua
authors: J
authors: Kimani
authors: Rupert
authors: R
authors: Kaul
authors: Nico J D
authors: NJ
authors: Nagelkerke
authors: Ma
authors: M
authors: Luo
authors: Kelly S
authors: KS
authors: MacDonald
authors: Elizabeth
authors: E
authors: Ngugi
authors: Keith R
authors: KR
authors: Fowke
authors: Blake T
authors: BT
authors: Ball
authors: Anthony
authors: A
authors: Kariri
authors: Jeckoniah
authors: J
authors: Ndinya-Achola
authors: Francis A
authors: FA
authors: Plummer
mesh_terms: D016022:Case-Control Studies; D015331:Cohort Studies; D018562:Disease Transmission, Infectious / Q000517:prevention & control; D005260:Female; D006069:Gonorrhea / Q000453:epidemiology; D015658:HIV Infections / Q000453:epidemiology*; D015497:HIV-1; D006801:Humans; D015994:Incidence; D007630:Kenya / Q000453:epidemiology; D015995:Prevalence; D040242:Risk Reduction Behavior; D011477:Sex Work; D012747:Sexual Partners; D047568:Unsafe Sex; D014504:Urban Health / Q000639:trends; D014505:Urban Population