How is HIV passed on?

HIV is found in the body fluids of an infected person. 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
by 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 an infected person, or donations of semen (artificial insemination), skin grafts and organ transplants. However, donated blood has been screened for HIV since 1985 in the UK. Similarly, screening is in place for organ and sperm donation.

Other factors that affect whether HIV is passed on

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 unprotected sex, for example.

There are factors that can affect the risk of it being passed on. These include:

viral load. Having a high viral load makes it more likely that you will pass on HIV
having another STI. If either partner has an STI, it is more likely that HIV will be passed on
the type of exposure. Sharing injecting equipment holds the highest risk of passing on HIV. Some sexual activities have a greater risk of HIV infection than others. (Find out more.)

Being on HIV treatment reduces your viral load and makes you less infectious.

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This article was last reviewed on 30/9/2012 by T. Kelaart

Date due for the next review: 30/9/2014

Content Author: S. Corkery (NAM)

Current Owner: S. Corkery (NAM)

More information:

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.
http://www.aidsmap.com/Treatment-is-prevention-HPTN-052-study-shows-96-reduction-in-transmission-when-HIV-positive-partner-starts-treatment-early/page/1879665/

www.aidsmap.com
HIV transmission http://www.aidsmap.com/HIV-transmission/page/1254898/

Protecting your own and other people’s sexual health http://www.aidsmap.com/Protecting-your-own-and-other-peoples-sexual-health/page/1255057/

www.aidsmap.com
How transmission occurs http://www.aidsmap.com/cms1320672.aspx

Co-factors that affect the risk of transmission http://www.aidsmap.com/cms1320688.aspx

Viral factors affecting transmission
http://www.aidsmap.com/cms1320689.aspx

Sexual activities http://www.aidsmap.com/cms1320690.aspx

Medical procedures http://www.aidsmap.com/cms1320694.aspx