* HIV is transmitted through penetrative (anal or vaginal) and oral sex; blood transfusion; the sharing of contaminated needles in health care settings and through drug injection; and, between mother and infant, during pregnancy, childbirth and breastfeeding.

2-1. Sexual transmission

HIV can be transmitted through unprotected penetrative sex. It is difficult to calculate the odds of becoming infected through sexual intercourse, however it is known that the risk of infection through vaginal sex is high. Transmission through anal sex has been reported to be 10 times higher than by vaginal sex. A person with an untreated sexually transmitted infection (STI), particularly involving ulcers or discharge, is, on average, 6-10 times more likely to pass on or acquire HIV during sex.

Oral sex is regarded as a low-risk sexual activity in terms of HIV transmission. Risk can increase if there are cuts or sores around or in the mouth and if ejaculation occurs in the mouth.

2-2. 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 injecting drug users by 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.

2-3. Mother-to-child transmission (MTCT)

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.

2-4. 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.