The bottom line

HIV can be transmitted through unprotected sexual intercourse, sharing injecting equipment or receiving blood transfusions and other blood–related products from an infected person. It can also be transmitted from an HIV-positive mother to her baby.

Unprotected sex

Established and common routes:

• Unprotected anal penetration
• Unprotected vaginal penetration.

Possible but less common routes:

• Oral transmission: it is now thought that between less than 1% to 3% of all HIV cases in the UK may be due to oral transmission. Most cases suggest that oral transmission depends on either damaged tissue in the mouth or throat, the presence of an untreated STI in the throat, or an ulceration on the penis.
• Any sexual activities where blood may be shared (e.g. involving piercing, shaving, etc).
• Through blood in otherwise uncontaminated body fluids: in the mouth or the rectum, during menstruation.
• Through shared sex toys etc.

Needles and sharps (non-medical)

Established and common route:

• Sharing injecting equipment.

Possible but less common route:

• Needle–stick and sharps injuries.

Possible but very uncommon route:

• Tattooing, acupuncture, electrolysis, shaving equipment. In these cases it is assumed that infection is possible but extremely unlikely. A case of infection through unsterilised acupuncture needles has been reported.

Medical (iatrogenic) transmission

Possible but less common routes:

• Unsterilised needles used for injection. This risk should be non-existent in the UK, but worldwide the World Health Organization (WHO) estimates that five per cent of HIV infections in developing countries are spread by this route.
• Blood transfusions, blood products and donations (organs, skin). Since 1985 blood donations in the UK have been screened, and screening began at roughly the same time in most other countries which could afford such programmes. Organs and tissues for donation have also been screened since that time, whilst blood products such as Factor VIII have been heat- treated since 1984.
• Surgical and other invasive procedures: fortunately very uncommon and the risk needs to be seen in the light of the far greater risks involved routinely in these invasive health care procedures.
• Occupationally through blood splashes onto broken skin and needle stick injuries.
• Donations of blood, organs, tissues, semen, breast milk and bone marrow – in each of these instances a very small number of cases have been reported.

Between mother and baby

• Through breastfeeding.
• During pregnancy and at birth.