title: Decline in HIV infectivity following the introduction of highly active antiretroviral therapy.
abstract: OBJECTIVE
  Little is known about the degree to which widespread use of antiretroviral therapy in a community reduces uninfected individuals' risk of acquiring HIV. We estimated the degree to which the probability of HIV infection from an infected partner (the infectivity) declined following the introduction of highly active antiretroviral therapy (HAART) in San Francisco.
  
  
  METHODS
  Homosexual men from the San Francisco Young Men's Health Study, who were initially uninfected with HIV, were asked about sexual practices, and tested for HIV antibodies at each of four follow-up visits during a 6-year period spanning the advent of widespread use of HAART (1994-1999).
  
  
  METHODS
  We estimated the infectivity of HIV (per-partnership probability of transmission from an infected partner) using a probabilistic risk model based on observed incident infections and self-reported sexual risk behavior, and tested the hypothesis that infectivity was the same before and after HAART was introduced.
  
  
  RESULTS
  A total of 534 homosexual men were evaluated. Decreasing trends in HIV seroincidence were observed despite increases in reported number of unprotected receptive anal intercourse partners. Conservatively assuming a constant prevalence of HIV infection between 1994 and 1999, HIV infectivity decreased from 0.120 prior to widespread use of HAART, to 0.048 after the widespread use of HAART- a decline of 60% (P=0.028).
  
  
  CONCLUSIONS
  Use of HAART by infected persons in a community appears to reduce their infectiousness and therefore may provide an important HIV prevention tool.
authors.affiliation: San Francisco Department of Public Health, Community Health and Epidemiology Section, San Francisco, CA, USA.
authors.forename: Travis C
authors.initials: TC
authors.lastname: Porco
authors.forename: Jeffrey N
authors.initials: JN
authors.lastname: Martin
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Page-Shafer
authors.forename: Amber
authors.initials: A
authors.lastname: Cheng
authors.forename: Edwin
authors.initials: E
authors.lastname: Charlebois
authors.forename: Robert M
authors.initials: RM
authors.lastname: Grant
authors.forename: Dennis H
authors.initials: DH
authors.lastname: Osmond
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D023241:Antiretroviral Therapy, Highly Active; D015331:Cohort Studies; D015483:HIV Antibodies / Q000032:analysis; D015658:HIV Infections / Q000453:epidemiology / Q000635:transmission*; D018451:Homosexuality, Male / Q000706:statistics & numerical data; D006801:Humans; D015994:Incidence; D008297:Male; D015233:Models, Statistical; D015995:Prevalence; D018570:Risk Assessment / Q000379:methods; D012309:Risk-Taking; D012495:San Francisco / Q000453:epidemiology; D012725:Sexual Behavior; D012747:Sexual Partners; D013997:Time Factors
chemical_list: D015483:HIV Antibodies