What is HIV?
HIV stands for human immunodeficiency virus. It is the virus that causes AIDS. When a person is infected with HIV, the virus enters the body and then resides and multiplies primarily in the white blood cells—the immune cells that normally protect us from disease.
AIDS stands for acquired immunodeficiency syndrome.
As HIV grows in an infected person, it damages or kills specific immune cells, weakening the immune system and leaving the person vulnerable to infections and illnesses ranging from pneumonia to cancer.
Only when someone with HIV begins to experience one or more of these conditions or loses a significant amount of immune cells are they diagnosed with AIDS.
How is HIV transmitted?
A person who has HIV carries the virus in certain body fluids, including blood, semen, vaginal secretions, and breast milk. A new HIV infection is established when a virus from these fluids encounters a cell that is susceptible to infection. Usually, HIV is transmitted through:
Unprotected sexual intercourse (either vaginal or anal) with someone who has HIV.
Sharing needles, syringes, or other injection equipment with someone who has HIV. HIV can survive in used syringes for a month or more. That’s why people who inject drugs should never reuse or share syringes or drug preparation equipment. This includes needles or syringes used to inject both legal and illegal drugs as well as other types of needles, such as those used for body piercing and tattoos.
Mother-to-child transmission during pregnancy, childbirth, or breastfeeding. Any woman who is pregnant or considering becoming pregnant should be tested for HIV. In the U.S., mother-to-infant transmission has dropped to just a few cases each year because pregnant women are routinely tested for HIV. Those who test positive can get drugs to prevent HIV from being passed on to their fetus or infant. If treated for HIV early in the pregnancy, a woman’s risk of transmitting HIV to her baby can be 1% or less. After delivery, she can prevent transmitting HIV to her baby by avoiding breastfeeding, since breast milk contains HIV.
In extremely rare cases, HIV has been transmitted by Oral sex—putting the mouth on the penis (fellatio), vagina (cunnilingus), or anus (rimming). In general, there’s little to no risk of getting HIV from oral sex. But transmission of HIV, though extremely rare, is theoretically possible if an HIV-positive man ejaculates in his partner’s mouth during oral sex.
Receiving blood transfusions, blood products, or organ/tissue transplants that are contaminated with HIV. This was more common in the early years of HIV, but now the risk is extremely small because of rigorous testing of the US blood supply and donated organs and tissues.
HIV Transmission Prevention
Today, more tools than ever are available to prevent HIV. You can use strategies such as abstinence (not having sex), limiting your number of sexual partners, never sharing needles, and using condoms the right way every time you have sex. You may also be able to take advantage of newer HIV prevention medicines such as pre-exposure prophylaxis (PrEP) and post-exposure prophylaxis (PEP).
If you have HIV, there are many actions you can take to prevent transmitting it to others. The most important is taking HIV medicine (called antiretroviral therapy, or ART) as prescribed. If you take HIV medicine as prescribed and get and keep an undetectable viral load (or stay virally suppressed), you can stay healthy and have effectively no risk of transmitting HIV to an HIV-negative sex partner.
Use condoms the right way every time you have sex Learn the right way to use a male condom.
Reduce your number of sexual partners. This can lower your chances of having a sex partner who will transmit HIV to you. The more partners you have, the more likely you are to have a partner with HIV whose viral load is not suppressed or to have a sex partner with a sexually transmitted disease. Both of these factors can increase the risk of HIV transmission.
Talk to your doctor about pre-exposure prophylaxis (PrEP), taking HIV medicines daily to prevent HIV infection, if you are at very high risk for HIV. PrEP should be considered if you are HIV-negative and in an ongoing sexual relationship with an HIV-positive partner. PrEP also should be considered if you aren’t in a mutually monogamous relationship with a partner who recently tested HIV-negative, andyou are a:
gay or bisexual man who has had anal sex without a condom or been diagnosed with an STD in the past 6 months;
man who has sex with both men and women; or
heterosexual man or woman who does not regularly use condoms during sex with partners of unknown HIV status who are at very high risk of HIV infection (for example, people who inject drugs or women who have bisexual male partners).
Post-exposure prophylaxis (PEP) means taking HIV medicines after being potentially exposed to HIV to prevent becoming infected. If you’re HIV-negative or don’t know your HIV status and think you have recently been exposed to HIV during sex (for example, if the condom breaks), talk to your health care provider or an emergency room doctor about PEP right away (within 3 days). The sooner you start PEP, the better; every hour counts. If you’re prescribed PEP, you’ll need to take it once or twice daily for 28 days. Keep in mind that your chance of getting HIV is lower if your HIV-positive partner is taking medicine to treat HIV infection (called antiretroviral therapy, or ART) as prescribed and his or her viral load stays undetectable (see Does my HIV-positive partner’s viral load affect my risk of getting HIV?).
If you’re HIV-negative and your partner is HIV-positive, encourage your partner to get and stay on treatment. If taken as prescribed, HIV medicine (ART) can make the amount of HIV in the blood (viral load) very low—so low that a test can’t detect it (called an undetectable viral load). People with HIV who get and keep an undetectable viral load can stay healthy for many years and have effectively no risk of transmitting HIV to an HIV-negative partner through sex.