The effects of viral load and antiretroviral medications on sexual transmission of HIV


Key take-home messages
  • Several studies have noted differences in viral load levels when comparing blood plasma to semen, cervicovaginal secretions and rectal mucosa.
  • Despite an undetectable blood plasma viral load (i.e. <50 copies/ml) a percentage of people living with HIV (as observed in cross-sectional studies), ranging from 5% to 25%, still have detectable viral loads in genital secretions.
  • Despite an undetectable blood plasma viral load, the presence of genital inflammation including sexually transmitted infections (STIs) and, for women, the use of hormonal contraceptives, correlates with a detectable viral load in genital secretions.
  • Some drugs included in Highly Active Antiretroviral Therapy (HAART) are not able to penetrate the genital tract; of those that can, only a small number do so effectively (i.e. suboptimal drug levels). This lack of penetration can be problematic as drug-resistant strains of HIV can replicate in the genital tract, which can act as separate compartment in the body, which means that virologic failure may not be detected in blood.
  • Rectal secretions were found to contain the highest levels of virus compared to blood plasma, vaginal and seminal fluids.
  • As blood plasma viral load was found to not accurately predict seminal vaginal and rectal mucosa viral loads, condom use is recommended during intercourse, even when people living with HIV have undetectable blood plasma viral loads.
  • Unprotected sexual intercourse among heterosexual serodiscordant couples in monogamous relationships, where the HIV-infected partner has full virologic suppression, carries minimal risk of HIV transmission.
  • Antiretroviral therapy is recommended for people with HIV in serodiscordant relationships to reduce the risk of HIV transmission to their uninfected partner.


The Ontario HIV Treatment Network: Rapid Response Service




  • Population(s)
    • General HIV+ population
  • Engagement and Care Cascade
    • Treatment


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