HIV transmission

Knowing how HIV is transmitted can enable you to take positive steps to protect yourself from acquiring the virus or, if you are HIV+, can help minimise the chances of you transmitting the virus on to anyone else.

HIV transmission is most likely to occur when an infected person’s blood, semen, pre-ejaculate/pre-cum, vaginal fluids or breast milk comes into contact with a non-infected person during the following activities:

  • unprotected penetrative sex, either anal or vaginal
  • injection or transfusion of contaminated blood or blood products, or receiving semen donation or an organ transplant from an HIV infected person
  • an HIV infected mother breastfeeding her child
  • an HIV infected mother passing the virus to her unborn child in utero or during labour
  • sharing unsterilised injection equipment with someone who is HIV+

The risk of HIV transmission through unprotected oral sex is low, although the risk is greater if you have any cuts, sores or abrasions in your mouth, if you are giving oral sex to an infected woman who is having her period, or if an infected man ejaculates in your mouth.

Although infected blood transfusions and organ donations have been a source of HIV transmission in the past, healthcare services are now well aware of the risk of transmission, so all organs and blood donations are now thoroughly screened for the virus.

Preventing HIV transmission

The risk of HIV transmission in sexual intercourse can be minimised by following a few simple steps—this advice will also help to protect you from other sexually transmitted infections:

  • Use condoms (male or female) every time you have vaginal or anal sex
  • Use a condom when giving oral sex to a man, or cover the female genitals and male or female anus with a latex or polyurethane (soft plastic) square during oral or oro-anal sex respectively
  • Avoid sharing sex toys—if you do share toys, wash them or cover them with a new condom when a new person uses them
  • If you have had unprotected sex with someone known to be HIV+ or you highly suspect is HIV+, you may be able to access PEP (post exposure prophylaxis) from one of our GUM clinics or an A&E Department—if this treatment is taken within 72 hours it may reduce the likelihood of being infected with HIV by approximately 80%
  • Regular screening for sexually transmitted infections—having some untreated STIs can increase your susceptibility to being transmitted HIV

If you are worried about HIV transmission and feel that you might be infected, you should have an HIV test as soon as possible. You can drop into any of our GUM clinics to do this. If you have been at risk of HIV it is likely you have been at risk of other STIs too so consider having a full STI screen as well as the HIV test.


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