title: Female-to-male infectivity of HIV-1 among circumcised and uncircumcised Kenyan men.
abstract: BACKGROUND
  A lack of male circumcision has been associated with increased risk of human immunodeficiency virus type 1 (HIV-1) acquisition in a number of studies, but questions remain as to whether confounding by behavioral practices explains these results. The objective of the present study was to model per-sex act probabilities of female-to-male HIV-1 transmission (i.e., infectivity) for circumcised and uncircumcised men, by use of detailed accounts of sexual behavior in a population with multiple partnerships.
  
  
  METHODS
  Data were collected as part of a prospective cohort study of HIV-1 acquisition among 745 Kenyan truck drivers. Sexual behavior with wives, casual partners, and prostitutes was recorded at quarterly follow-up visits. Published HIV-1 seroprevalence estimates among Kenyan women were used to model HIV-1 per-sex act transmission probabilities.
  
  
  RESULTS
  The overall probability of HIV-1 acquisition per sex act was 0.0063 (95% confidence interval, 0.0035-0.0091). Female-to-male infectivity was significantly higher for uncircumcised men than for circumcised men (0.0128 vs. 0.0051; P=.04). The effect of circumcision was robust in subgroup analyses and across a wide range of HIV-1 prevalence estimates for sex partners.
  
  
  CONCLUSIONS
  After accounting for sexual behavior, we found that uncircumcised men were at a >2-fold increased risk of acquiring HIV-1 per sex act, compared with circumcised men. Moreover, female-to-male infectivity of HIV-1 in the context of multiple partnerships may be considerably higher than that estimated from studies of HIV-1-serodiscordant couples. These results may explain the rapid spread of the HIV-1 epidemic in settings, found throughout much of Africa, in which multiple partnerships and a lack of male circumcision are common.
authors.affiliation: Department of Epidemiology, University of Washington, Seattle, Washington 98104-2499, USA. jbaeten@u.washington.edu
authors.forename: Jared M
authors.initials: JM
authors.lastname: Baeten
authors.forename: Barbra A
authors.initials: BA
authors.lastname: Richardson
authors.forename: Ludo
authors.initials: L
authors.lastname: Lavreys
authors.forename: Joel P
authors.initials: JP
authors.lastname: Rakwar
authors.forename: Kishorchandra
authors.initials: K
authors.lastname: Mandaliya
authors.forename: Job J
authors.initials: JJ
authors.lastname: Bwayo
authors.forename: Joan K
authors.initials: JK
authors.lastname: Kreiss
mesh_terms: D000328:Adult; D002944:Circumcision, Male; D015658:HIV Infections / Q000453:epidemiology* / Q000635:transmission* / Q000821:virology; D006801:Humans; D007630:Kenya / Q000453:epidemiology; D008297:Male; D011446:Prospective Studies; D012307:Risk Factors; D012725:Sexual Behavior