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Factors Increasing the Risk of Acquiring or Transmitting HIV

The following tables provide estimates for key risk factors that increase risk of acquiring or transmitting HIV as identified in the published scientific literature.

Ulcerative STD Infection of HIV-Negative Persons

Population HIV Risk Estimate Source Interpretation
Heterosexual Men and Women 2.65 Hughes 2012 Having an STD more than doubles the risk of an HIV-negative heterosexual person of acquiring HIV during sex with an HIV-positive heterosexual partner.
MSM 2.65 Hughes 2012 There are no empirical data providing a direct estimate for MSM. Biological and epidemiological theories provide indirect evidence that ulcerative STD infection has similar effects on HIV risk in MSM.

Having an STD may more than double the risk of an HIV-negative MSM of acquiring HIV during sex with an HIV-positive MSM partner.

Strengths and Limitations of Risk Estimates:

  • Hughes, 2012 is a longitudinal cohort study of 3,297 discordant heterosexual African couples, with 86 confirmed linked HIV transmissions. This risk estimate for ulcerative STDs is specific to genital ulcer disease among HIV-negative partners, where genital ulcer disease includes genital herpes (due to HSV-1 or HSV-2), syphilis, and chancroid.
  • The evidence supports an increased risk of HIV acquisition when the uninfected partner has an STD. It is unclear, however, what the most appropriate estimates are for each population, behavior, and type of STD given the observational nature of these kinds of studies. Several studies have found that ulcerative STDs may confer higher risk (e.g., risk ratio ranges from 2.2 to 11.3) than non-ulcerative, inflammatory STDs (e.g. risk ratio ranges from 3 to 4) (Fleming, 1999; Galvin, 2004; Berman, 2006). However, an updated systematic review of the published literature is needed for more accurate risk estimates by population, behavior, and type of STD.
  • Although no direct empirical evidence has been identified for MSM at this time, it is biologically and epidemiologically plausible for STDs to also increase the risk of HIV acquisition among HIV-negative MSM. The estimate for heterosexual men and women is the best proxy estimate for MSM until more direct evidence is available.

Source:

  • Hughes JP, Baeten JM, Lingappa JR, et al. Determinants of per-coital-act HIV-1 infectivity among African HIV-1-serodiscordant couples. J Inf Dis 2012;205(3):358-65.
  • Fleming DT, Wasserheit JN. From epidemiological synergy to public health policy and practice: the contribution of other sexually transmitted diseases to sexual transmission of HIV infection. Sex Trans Infect 1999; 75(1):3–17.
  • Galvin SR & Cohen MS. The role of sexually transmitted diseases in HIV transmission. Nature Reviews: Microbiology 2004;2(1):33-42.
  • Berman SM & Cohen MS. STD treatment: How can it improve HIV prevention in the South? Sex Trans Dis 2006;33:S50-S57.

Ulcerative STD Infection of HIV-Positive Persons

Population HIV Risk Estimate Source Interpretation
Heterosexual Men and Women 2.58 Gray 2001 Having an STD more than doubles the risk of an HIV-positive heterosexual man or women to transmit HIV during sex to his/her uninfected heterosexual partner.
MSM 2.58 Gray 2001 There are no empirical data providing a direct estimate for MSM. Biological and epidemiological theories provide indirect evidence that ulcerative STD infection has similar effects on HIV risk among MSM.

Having an STD more than doubles the risk of an HIV-positive heterosexual man or women transmitting HIV during sex to his/her uninfected heterosexual partner.

Strengths and Limitations of Risk Estimates:

  • Gray, 2001 is a longitudinal cohort study of 174 monogamous discordant heterosexual couples, with 38 HIV transmissions to uninfected partners, from a larger Rakai (Uganda) community-randomized trial of STD control for AIDS prevention. This risk estimate for ulcerative STDs is specific to the presence of genital ulceration.
  • The evidence suggests an increased risk of HIV transmission due to the HIV-positive partner having an STD.  It is unclear, however, what the most appropriate estimates are for each population, behavior, and type of STD given the observational nature of these kinds of studies.  Indirect evidence of STDs increasing the infectiousness of HIV exist. Ulcerative STDs generally increase HIV shedding in the genital tract and inflammatory STDs increase the concentration of HIV in the urethra, semen, and cervical fluid (Galvin, 2004). An updated systematic review of the published literature is needed for more accurate risk estimates by population, behavior, and type of STD.
  • Although no direct empirical evidence has been identified for MSM at this time, it is biologically and epidemiologically plausible for STDs to also increase the risk of HIV transmission among HIV-positive MSM. The estimate for heterosexual men and women is the best proxy estimate for MSM until more direct evidence is available.

Source:

  • Galvin SR & Cohen MS. The role of sexually transmitted diseases in HIV transmission. Nature Reviews: Microbiology 2004;2(1):33-42.
  • Gray RH, Wawer MJ, Brookmeyer R, et al. Probability of HIV-1 transmission per coital act in monogamous, heterosexual, HIV-1-discordant couples in Rakai, Uganda. Lancet 2001;357:1149-53.

Acute HIV Infection

Population HIV Risk Estimate Source Interpretation
Heterosexual Men and Women 7.25 Wawer, 2015 The risk of HIV transmission during acute infection is about 7.25 times the risk during the middle stage of HIV disease among heterosexual men and women.
MSM 7.25 Wawer, 2015 There are no empirical data providing a direct estimate for MSM. It is biologically plausible for acute infection to have a similar effect on HIV transmission among MSM.

The risk of HIV transmission during acute infection is about 7.25 times the risk during the middle stage of HIV disease among MSM.

Strengths and Limitations of Risk Estimates:

  • Wawer, 2015 estimates the increased risk of HIV transmission due to acute HIV infection from a retrospective sub-sample of 235 monogamous, HIV-discordant heterosexual couples with follow up time from a larger Rakai (Uganda) community-randomized trial of STD control for AIDS prevention. This study looked at early-stage infection (defined as up to 5 months after seroconversion, a 2.5-month midpoint), established infection or “middle” stage of infection (>6 months after seroconversion), and late-stage infection (6 to 25 months before death).
  • No other published study of empirical data on increased risk of HIV transmission during acute infection exists.
  • Acute HIV infection is clinically defined as the time between viral infection and development of detectable antibodies against HIV-1.  During this time, concentrations of HIV in blood and semen are highest and transmission risk is therefore greatest; this period typically last a few weeks (Cohen, 2005; Pilcher, 2004).  Pilcher, 2007 estimated that viral load reaches its peak at 17 days after seroconversion in blood and around 4 weeks after seroconversion in semen. A modeling paper (Pilcher, 2004) estimated the probability of heterosexual transmission of HIV during acute infection is ~8 to10 times the probability  during later stage of infection, where the viral load peak in semen was modeled at about day 20 after infection.
  • Although no direct empirical evidence has been identified for MSM at this time, acute infection is likely to also be associated with increased HIV transmission risk among MSM. The estimate for heterosexual men and women is the best proxy estimate for MSM until more direct evidence is available.

Source:

  • Cohen MS & Pilcher CD. Amplified HIV transmission and new approaches to HIV prevention. J Infect Dis 2005;191:1391-3.
  • Pilcher CD, Tien HC, Eron JJ Jr, et al. Quest Study, Duke-UNC-Emory Acute HIV Consortium. Brief but efficient: acute HIV infection and the sexual transmission of HIV. J Infect Dis 2004; 189(10):1785–92.
  • Pilcher CD, Joaki G, Hoffman IF, et al. Amplified transmission of HIV-1: comparison of HIV-1 concentrations in semen and blood during acute and chronic infection. AIDS 2007;21(13):1723-30.
  • Wawer MJ, Gray RH, Sewankambo NK, et al. Rates of HIV-1 transmission per coital act, by stage of HIV-1 infection, in Rakai, Uganda. J Infect Dis 2005;191:1403-9.
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