Transmission through Sexual Contact

One of the most common ways HIV is transmitted is through sexual contact, primarily through unprotected vaginal or anal intercourse. In every act of sexual penetration, there is an inserter and a receiver. The receiver is generally at greater risk than the inserter, although if the penis of the inserter has open cuts, sores, or ulcers, then the inserter’s risk will be increased.

Unprotected anal sex (penetration of the anus by the penis) between two men or between a man and a woman is particularly risky because the chance of damage (small tears and lesions) to the thin lining of the rectum is high. This facilitates HIV transmission by enabling the virus in semen to quickly enter the bloodstream.

With penile-vaginal sex, the female partner is generally at greater risk because of the greater exposed surface area in the female genital tract than in the male genital tract, the higher concentrations of HIV in seminal fluids than in vaginal fluids, and the larger amount of semen than vaginal fluids exchanged during intercourse.

Although HIV transmission through unprotected oral sex—cunnilingus (oral-vulva contact) or fellatio (oral-penile contact)—can occur, the risk is much lower than for unprotected vaginal or anal sex. But this behavior is not free of risk. With oral sex, the person at greater risk is the one using his or her mouth to stimulate the other person’s genitals. The risk is increased when that person has open sores in the mouth or bleeding gums. The risk is also increased when that person receives semen in the mouth or swallows any secretions.

HIV transmission has also been reported through infected semen used for artificial insemination. Reputable sperm banks now test all samples before using them.

If both partners in a relationship know that they are not infected and they are monogamous (which is difficult to know), there will be no risk for HIV transmission during unprotected sex.

HIV risk and contraception

Contraceptive methods other than male or female condoms are not effective against the transmission of STIs, including HIV. Recent research results indicate that women who use some hormonal contraceptives (oral contraceptives or Depo-Provera) have an increased risk for contracting some STIs/RTIs but a decreased risk for contracting others. For example, women using oral contraceptives were at increased risk for chlamydia and vaginal yeast infections, but decreased risk for bacterial vaginosis compared with women not using family planning. This altered susceptibility to STIs could influence HIV transmission.

Some concern also exists about the possibility of hormonal contraceptives increasing HIV susceptibility due to endometrial, cervical mucus, or bleeding changes that can occur with use of these methods. Some evidence suggests that methods with higher levels of progestins may increase risk; however, other studies had mixed results. Additional research on this topic is needed. Women who use hormonal methods are less likely to use condoms, so it is important to reach these women with counseling messages promoting dual-method use (i.e., hormonal methods for pregnancy prevention and condom use for prevention of infection).

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