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How is HIV passed on?

how hiv is passed on

HIV is found in the body fluids of a person living with HIV. There may be enough HIV to be infectious in semen, genital fluids*, blood and breast milk.

*Definition of genital fluids: Vaginal and cervical secretions, semen (cum), pre-ejaculate (pre-cum) and rectal secretions

To pass on the virus, infected body fluids need to get into someone else’s bloodstream.

The main ways in which HIV is passed on are:

  • unprotected anal or vaginal sex - the risk from oral sex is lower but still exists
  • sharing injecting equipment
  • from a mother to her baby during pregnancy or birth, or when breastfeeding.

HIV can be passed on by receiving blood transfusions or other blood-related products from someone living with HIV, or donations of semen (artificial insemination), skin grafts and organ transplants. However, in the UK, donated blood has been screened for HIV since 1985. Similarly, screening is in place for organ and sperm donation.

Other risk factors

HIV isn’t actually as infectious as many other sexually transmitted infections (STIs). It isn’t automatically passed on every time a positive and a negative person have condomless sex, for example.

Other factors that can affect the risk of HIV being passed on:

If you’re on HIV treatment, there is an extremely low risk of you passing HIV to your partner through unprotected vaginal or anal sex as long as:

  1. neither you nor your partner have an STI, and
  2. you’ve had a stable undetectable viral load for at least six months.

Condoms are still the best way to prevent the spread of STIs.

Before you make any decision about not using condoms, get advice from your HIV doctor or nurse.

More about HIV:

Next: How is HIV not passed on? ››

‹‹ Previous: The stages of HIV infection



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This article was last reviewed on 23/11/2015 by Anna Peters

Date due for the next review: 23/11/2018

Content Author: Kerri Virani

Current Owner: Kerri Virani

More information:

STIs make no difference to transmission risk in those with suppressed viral load: Davies O et al. Impact of rectal gonorrhoea and chlamydia on HIV viral load and inflammatory markers in the rectum; potential significance for onward transmission. BHIVA conference, Thursday 23 April 2015, abstract O19

Impact of rectal Gonorrhoea and Chlamydia on HIV viral load in the rectum; potential significance for onward transmission, Olubanke Davies, Sinead Costelloe, Juan Tiraboschi, John White, Siobhan O’Shea, Julie Fox, Presentation from BHIVA conference 21-24 April 2015

Men taking HIV treatment have undetectable viral loads in the rectum; sexually transmitted infections make no difference, NAM, Aidsmap, Roger Pebody, 24/4/15

Condoms, NHS Choices, 13/1/15

Wu L Biology of HIV mucosal transmission. Curr Opin HIV AIDS 3(5): 534-540, 2008

Ho DD et al. Quantitation of human immunodeficiency virus type 1 in the blood of infected persons. N Engl J Med 321:1621-1625, 1989

Pudney J et al. Pre-ejaculatory fluid as potential vector for sexual transmission of HIV-1. Lancet 340: 1470, 1992

Fiore JR et al. Correlates of HIV-1 shedding in cervicovaginal secretions and effects of antiretroviral therapies. AIDS 17: 2169-2176, 2003

Neely MN et al. Cervical shedding of HIV-1 RNA among women with low levels of viremia while receiving highly active antiretroviral therapy. Acqir Immune Defic Syndr 44: 38-42, 2007

Zuckerman RA et al. Higher concentrations of HIV RNA in rectal mucosa secretions than in blood and seminal plasma, among men who have sex with men, independent of antiretroviral therapy. J Infect Dis 189: 156-161, 2004

Ziegler JB et al. Postnatal transmission of AIDS-associated retrovirus from mother to infant. Lancet 1: 896-898, 1985

Cohen M et al. Antiretroviral treatment to prevent the sexual transmission of HIV-1: results from the HPTN 052 multinational randomized controlled ART. Sixth International AIDS Society Conference on HIV Pathogenesis, Treatment and Prevention, Rome, abstract MOAX0102, 2011.