The risk of HIV transmission varies widely by the type of exposure. Anal intercourse for both receptive and insertive partners has a higher risk versus vaginal intercourse, and vaginal intercourse is a higher risk act compared to oral intercourse. Also, receptive intercourse (both vaginal and anal) has an increased risk compared to insertive intercourse. Generally, the risk of HIV transmission for receptive anal intercourse, receptive vaginal intercourse and receptive oral intercourse is 0.5%, 0.1% and 0.01% per act, respectively. However, the risk varies widely depending on differences in factors such as co-occurrence with other sexually transmitted infections (STIs), level of viral load, stage of disease, and circumcision. Plasma viral load is considered as the strongest determinant of sexual transmission of HIV.
Higher rates of infection with HIV are exhibited among injection drug users mainly because of unsafe injecting behavior. The risk of HIV transmission per each drug injection is 0.67%.
Vertical transmission may occur during pregnancy by micro-transfusion of blood across the placenta; or during labor and delivery by the exposure of neonate with maternal blood and genital tract secretions, and after the birth through breastfeeding. It is estimated that 24-45% of HIV infected mothers transmit the virus to their offspring if there is no intervention. Maternal plasma viral load, co-infection with STIs, chorioamnionitis, concurrent HCV infection or active tuberculosis, and vaginal versus caesarean delivery are associated with the increased risk of vertical transmission. Contributing factors to mother to child transmission include breastfeeding pattern and duration, health status of maternal breast, and high plasma or breast milk viral load.
Keywords: Anal intercourse, HIV exposure, HIV sexual transmission, HIV transmission, HIV viral load, Mother to child HIV transmission, Oral intercourse, People who Inject Drugs, Risk of HIV transmission, Route of HIV transmission, Sexually Transmitted Infections, Vaginal intercourse, Vertical transmission.