Risk of HIV Transmission via Sexual Contact:

• Vaginal Intercourse:
  • Estimated risk per act: ~0.08% (range: 0.04–0.13%) for receptive partner, ~0.04% for insertive partner.
  • Rationale: Higher risk for receptive partner due to greater mucosal exposure.
• Anal Intercourse:
  • Estimated risk per act: ~1.42% (range: 0.62–2.22%) for receptive partner, ~0.06% for insertive partner.
  • Rationale: Higher risk due to delicate rectal mucosa and potential for microtears.
• Oral Sex:
  • Estimated risk per act: ~0.04% (range: 0.00–0.04%) for receptive partner, negligible for insertive partner.
  • Rationale: Lower risk due to fewer mucosal breaks and lower viral loads in saliva.
• Modifying Factors:
  • Higher Risk: Genital ulcers (e.g., HSV, syphilis), STIs, bleeding, or trauma.
  • Lower Risk: Effective ART (viral suppression), PrEP, PEP, or condom use.

• Key Mechanisms:
  • HIV is present in genital secretions (semen, vaginal fluid) and blood.
  • Transmission occurs via mucosal contact with infected fluids, facilitated by breaks in mucosal integrity.

• Guidelines:
  • CDC: Condoms reduce risk by ~70–80% when used consistently and correctly.
  • WHO: ART for HIV+ individuals reduces transmission risk to near zero when viral load is undetectable.

• Research Evidence:
  • HPTN 052 trial: ART reduced HIV transmission in discordant couples by 96%.
  • PARTNER study: No linked transmissions in couples where HIV+ partner had undetectable viral load.