What is the probability of HIV transmission through various routes?

HIV transmission occurs through specific routes involving direct contact with certain infectious bodily fluids—primarily blood, semen, vaginal fluids, rectal fluids, and breast milk—from a person living with HIV who has a detectable viral load. The risk of transmission varies significantly depending on the exposure type, viral load, presence of other sexually transmitted infections, mucosal integrity, and use of preventive interventions.

Per-act transmission probabilities (estimated from epidemiologic studies) are as follows: receptive anal intercourse carries the highest risk—approximately 1.4% per exposure; insertive anal intercourse is lower at about 0.11%. For vaginal intercourse, the estimated risk is roughly 0.08% per act for the receptive partner and 0.04% for the insertive partner. Sharing needles or syringes for injection drug use carries an estimated risk of 0.63% per use. Mother-to-child transmission without intervention ranges from 15–45%, but this drops to less than 1% with appropriate antiretroviral therapy, cesarean delivery when indicated, and avoidance of breastfeeding in resource-rich settings.

Importantly, no documented cases of HIV transmission have occurred through casual contact—including hugging, shaking hands, sharing food or utensils, toilet seats, swimming pools, or insect bites. Saliva, tears, and sweat do not contain sufficient concentrations of HIV to cause infection. Additionally, effective antiretroviral therapy that achieves and maintains viral suppression (undetectable viral load) eliminates the risk of sexual transmission—this is the foundation of the “Undetectable = Untransmittable” (U=U) scientific consensus.

Prevention strategies such as consistent condom use, pre-exposure prophylaxis (PrEP), post-exposure prophylaxis (PEP), sterile needle exchange, and routine HIV testing remain critical components of comprehensive HIV prevention. Accurate risk assessment should always consider individual clinical and behavioral context—and consultation with a healthcare provider is recommended for personalized guidance.