Differences in HIV Transmission Risk
Reviewed by: HU Medical Review Board | Last reviewed: September 2019
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
Figure 1. Estimated HIV transmission risk by method of sexual transmission
| 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
Figure 2. Estimated HIV transmission risk by other methods of transmission
| 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