HIV is transmitted through penetrative (anal or vaginal) sex, blood transfusion, the sharing of contaminated needles in health-care settings and drug injection and between mother and infant during pregnancy, childbirth and breastfeeding.
HIV can be transmitted through penetrative sex. HIV is not transmitted very efficiently so the risk of infection through a single act of vaginal sex is low. Transmission through anal sex has been reported to be 10 times higher than by vaginal sex. A person with an untreated sexually transmitted infection, particularly involving ulcers or discharge, is, on average, six to 10 times more likely to pass on or acquire HIV during se
Oral sex is regarded as a low-risk sexual activity in terms of HIV transmission.
When a person living with HIV is taking effective antiretroviral therapy and has a suppressed viral load they are no longer infectious.
Transmission through sharing of needles and syringes
Re-using or sharing needles or syringes represents a highly efficient way of transmitting HIV. The risk of transmission can be lowered substantially among people who inject medicines by always using new needles and syringes that are disposable or by properly sterilizing reusable needles/syringes before reuse. Transmission in a health-care setting can be lowered by health-care workers adhering to universal precautions.
HIV can be transmitted to an infant during pregnancy, labour, delivery and breastfeeding. Generally, there is a 15–30% risk of transmission from mother to child before and during delivery. A number of factors influence the risk of infection, particularly the viral load of the mother at birth (the higher the load, the higher the risk). Transmission from mother to child after birth can also occur through breastfeeding (see question 21). The chances of transmission of HIV to a child is very low if the mother is on antiretroviral therapy during pregnancy and when breastfeeding.
Transmission through blood transfusion
There is a high risk (greater than 90%) of acquiring HIV through transfusion of infected blood and blood products. However, the implementation of blood safety standards ensures the provision of safe, adequate and good-quality blood and blood products for all patients requiring transfusion. Blood safety includes screening of all donated blood for HIV and other blood-borne pathogens, as well as appropriate donor selection.