title: Estimating per-act HIV transmission risk: a systematic review.
abstract: BACKGROUND
  Effective HIV prevention programs rely on accurate estimates of the per-act risk of HIV acquisition from sexual and parenteral exposures. We updated the previous risk estimates of HIV acquisition from parenteral, vertical, and sexual exposures, and assessed the modifying effects of factors including condom use, male circumcision, and antiretroviral therapy.
  
  
  METHODS
  We conducted literature searches to identify new studies reporting data regarding per-act HIV transmission risk and modifying factors. Of the 7339 abstracts potentially related to per-act HIV transmission risk, three meta-analyses provided pooled per-act transmission risk probabilities and two studies provided data on modifying factors. Of the 8119 abstracts related to modifying factors, 15 relevant articles, including three meta-analyses, were included. We used fixed-effects inverse-variance models on the logarithmic scale to obtain updated estimates of certain transmission risks using data from primary studies, and employed Poisson regression to calculate relative risks with exact 95% confidence intervals for certain modifying factors.
  
  
  RESULTS
  Risk of HIV transmission was greatest for blood transfusion, followed by vertical exposure, sexual exposures, and other parenteral exposures. Sexual exposure risks ranged from low for oral sex to 138 infections per 10,000 exposures for receptive anal intercourse. Estimated risks of HIV acquisition from sexual exposure were attenuated by 99.2% with the dual use of condoms and antiretroviral treatment of the HIV-infected partner.
  
  
  CONCLUSIONS
  The risk of HIV acquisition varied widely, and the estimates for receptive anal intercourse increased compared with previous estimates. The risk associated with sexual intercourse was reduced most substantially by the combined use of condoms and antiretroviral treatment of HIV-infected partners.
authors.affiliation: Division of HIV/AIDS Prevention, National Center for HIV, Viral Hepatitis, STD, and TB Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
authors.forename: Pragna
authors.initials: P
authors.lastname: Patel
authors.forename: Craig B
authors.initials: CB
authors.lastname: Borkowf
authors.forename: John T
authors.initials: JT
authors.lastname: Brooks
authors.forename: Arielle
authors.initials: A
authors.lastname: Lasry
authors.forename: Amy
authors.initials: A
authors.lastname: Lansky
authors.forename: Jonathan
authors.initials: J
authors.lastname: Mermin
mesh_terms: D018562:Disease Transmission, Infectious; D015658:HIV Infections / Q000635:transmission*; D006801:Humans; D007049:Iatrogenic Disease / Q000453:epidemiology; D018445:Infectious Disease Transmission, Vertical; D009034:Mother-Child Relations; D018570:Risk Assessment; D012725:Sexual Behavior