HIV transmission

HIV can be transmitted through the blood (including menstrual blood), semen, breast milk, and vaginal fluids/secretions of infected persons. Transmission to another person can occur if those fluids enter the other person's body. HIV can be isolated from other bodily fluids, such as saliva, sweat, and tears, but the viral concentration is so low that the transmission risk is negligible. HIV cannot be transmitted from coughing or sneezing, sharing household items, or swimming in a pool with someone who is infected.

Transmission is affected by viral fitness (ability of the virus to replicate and cause disease), amount of exposure, and host resistance. There are three main ways in which HIV is transmitted.

Through unprotected anal or vaginal sex. The presence of another sexually transmitted infection (such as an active case of herpes or syphilis) heightens the risk of HIV transmission, as does unprotected sex with someone in the primary (acute) stage of HIV infection. HIV is unable to pass through quality latex or polyurethane condoms.

Through blood-to-blood contact. This mainly happens through the sharing of injecting equipment among drug users. The risk of transmission is high whenever needles and syringes are shared or re-used without proper sterilisation.

Very rarely, HIV infection results from an occupational accident amongst healthcare workers. Fortunately, follow-up studies have shown that 99.7% of all reported needlestick/cut exposures do not lead to HIV infection.

In countries where the blood supply is not screened, transmission occurs through the use of infected blood and blood products. In the past, infected blood products such as the Factor VIII used to treat haemophilia were responsible for causing many HIV infections.

Vertically, from an HIV-positive mother to her baby while pregnant, giving birth, or breastfeeding. In the absence of antiretroviral therapy, the average risk of transmission during pregnancy or delivery is in the region of 10 to 15%, although it will be higher if the mother has primary infection, a high viral load, or has developed AIDS. Breastfeeding carries a risk of transmission and should be avoided if alternatives to breastfeeding (including a safe water supply) are available and affordable.