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Differences in HIV Transmission Risk

HIV can affect anyone who has a potentially virus-transmitting experience, such as having unprotected sex with an HIV-positive partner without being on medication to control the virus or prevent its transmission. Although there are several possible situations in which the virus can be transmitted, not all of these situations carry the same risk. Some behaviors carry a higher risk of transmission for those engaging in them when compared to others. However, when looking at HIV transmission risks, it’s important to remember that these are just averages and estimates. The actual transmission rate can vary from person to person, and scenario to scenario.1

Sexual acts and transmission risks

Common sexual acts and their estimated transmission rates, assuming exposure to HIV occurred during the act, include the following:1-3

Method of transmission Estimated transmission risk
Receptive* anal intercourse (bottoming) 1.38 percent
Insertive* anal intercourse (topping) 0.11 percent
Receptive penile-vaginal intercourse 0.08 percent
Insertive penile-vaginal intercourse 0.04 percent
Receptive oral sex Low (less than 0.04 percent)
Insertive oral sex Low (less than 0.04 percent)

*Receptive sexual acts refer to the partner being penetrated, and insertive sexual acts refer to the partner doing the penetrating.

Other common terms for oral sex include, but are not limited to, fellatio, blowjob, giving head (when involving the penis), cunnilingus, eating out (when involving the vagina), anilingus, or rimming (when involving the anus).

Other potential transmission scenarios

HIV is not only transmitted through sexual contact. There are other ways in which the virus may be transmitted if it’s present. Some of these situations and their accompanying risks include:1-3

Method of transmission Estimated transmission risk
Needle-sharing injection drug use 0.63 percent
Percutaneous needle stick
(accidental needle stick)
0.23 percent
Mother-to-child transmission 22.6 percent**
Biting Negligible (incredibly low)
Throwing bodily fluids (like semen) Negligible (incredibly low)
Sharing sex toys Negligible (incredibly low)

**It’s important to note that transmission risk estimates for mother-to-child transmission are determined only from expectant mothers with the virus, and not all expectant mothers.

The highest risk of getting HIV actually comes from being exposed to blood containing the virus during a blood transfusion (92.5 percent).1-3 This was more of a concern in the past when blood products and donated organs were not screened for HIV and other blood-borne diseases. Today, the donated blood supply and donated organs are thoroughly screened for HIV, and the risk of receiving a blood or organ donation that is HIV-positive is incredibly low.4

Factors that can change risk estimates

As mentioned, these numbers are estimates based on the average risk for all individuals. However, there are some factors that can increase or decrease an individual’s risk of getting or transmitting the virus. For example, the presence of another co-occurring sexually transmitted infection (STI), such as herpes, can increase an individual’s risk of transmitting or getting HIV. Any sexual contact that involves blood, including open sores, tears during sex, or menstrual bleeding, may increase the risk of HIV transmission. On the other hand, using condoms or taking medications to control HIV can decrease the risk of transmission.4-7

There are other factors that can impact the risk of getting HIV from non-sexual acts. These include sterilizing needles when participating in intravenous drug use, or practicing safe disposal of needles used in hospitals or other healthcare settings.8 Pregnant women should be tested for HIV, and can decrease the risk of transmitting the virus to their baby if they start HIV-controlling medications.9

Written by: Casey Hribar | Last reviewed: September 2019
  1. Per-Act Risk of HIV Transmission. Public Health Agency of Canada: CATIE. https://www.catie.ca/en/hiv-canada/4/4-1/4-1-2. Accessed June 15, 2019.
  2. Patel P, Borkowf CB, Brooks JT, et al. Estimating per-act HIV transmission risk: A systematic review. AIDS. 19 Jun 2014; 28(10), 1509-1519. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6195215/. Accessed June 15, 2019.
  3. HIV Risk Behaviors. Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/risk/estimates/riskbehaviors.html. Published December 4, 2015. Accessed June 15, 2019.
  4. HIV Transmission. Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/basics/transmission.html. Published October 31, 2018. Accessed June 15, 2019.
  5. HIV 101. United States Department of Health and Human Services: Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/pdf/workplace/cdc-hiv101.pdf. Accessed June 15, 2019.
  6. Corkery S. Factsheet: Herpes. National AIDS Manual (NAM) AIDSmap. http://www.aidsmap.com/Herpes/page/1044860/. Published November 2017. Accessed June 15, 2019.
  7. Oral Sex and HIV Risk. Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/risk/oralsex.html. Published July 8, 2016. Accessed June 15, 2019.
  8. Injection Drug Use and HIV Risk. Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/risk/idu.html. Published May 28, 2019. Accessed June 15, 2019.
  9. Mother-To-Child Transmission of HIV. World Health Organization. https://www.who.int/hiv/topics/mtct/about/en/. Accessed June 15, 2019.