Misunderstandings about how human immunodeficiency virus (HIV) can spread are common, which may lead to questions about whether it’s possible to get HIV even if you and your partner are HIV-negative.

It’s not possible to contract HIV if you and your partner are HIV-negative, have been properly tested, and have had no recent exposure to the virus. However, if either of you has had an exposure but tested negative, it may still be possible to spread the virus, because it’s possible the testing was done too early and missed the infection.

Knowing when to test for HIV and what you can do to help prevent exposures can ensure you and your partner remain negative.

How Is HIV Transmitted?

The first step in HIV prevention is understanding how the virus spreads. The virus can be spread only through contact with an HIV-positive person’s bodily fluids (blood, semen, vaginal or rectal fluids, or breast milk). Possible exposure may occur through:

• Engaging in unprotected anal or vaginal sex
• Sharing needles or syringes with an HIV-positive person
• Receiving a blood transfusion — Although the risk here is extremely low in countries such as the U.S. where blood is carefully screened for HIV and other infectious agents

The more sexual partners a person has, the greater their risk of contracting HIV will be. It is less common to spread HIV through an accidental needlestick (more likely to occur in health care workers) or from a pregnant person to their fetus, especially if the mother is receiving treatment.

Can You Get HIV if Your Partner Is HIV-Negative?

An uninfected person cannot spread HIV. However, a person can have an exposure and become positive without knowing it, or someone can test negative before the test detects the infection. It’s important to know when to test to get the most accurate results.

How Long Does It Take HIV To Become Detectable?

HIV cannot be detected immediately after exposure. After the virus enters your body, it takes time for the immune system to recognize it’s there and to build up a response. Antibodies targeting HIV take a few weeks to develop, which means that tests that depend on identifying these antibodies (like most rapid tests) cannot detect the virus until then. If you take one of these tests before this time period, you may receive a false-negative result, meaning that your test reads negative although you might still be infected with HIV.

Nucleic acid tests (NATs) for HIV detect the actual genetic material (RNA) of the HIV virus, so they don’t depend on the immune system to build a response. However, NAT tests are not considered reliable until about 10 days after exposure, because it takes that long for the virus to reproduce enough for the test to find it in the blood.

An antigen/antibody test can detect an HIV protein called p24 antigen, which means it does not always have to wait for an antibody response to detect HIV. This type of test is commonly used in hospitals and clinics in the United States and is considered reliable sooner after exposure than an antibody-only test.

HIV Testing After an Exposure

After a potential HIV exposure, there is a “window period” for HIV testing. This refers to the period of time between the initial exposure and when a test can first detect the virus or antibodies to the virus. Each test has a different window period, so it’s important that you note when the exposure occurred. This helps make sure the test used is as accurate as possible for detecting HIV.

According to the Centers for Disease Control and Prevention (CDC), the window periods for the various tests are as follows:

• For NATs, which detect the actual virus, the window is 10 to 33 days after exposure.
• For antigen/antibody tests from a blood draw, the window is 18 to 45 days after exposure.
• For rapid antigen/antibody tests from a finger stick, the window is 18 to 90 days after exposure.
• For antibody tests (which are most rapid tests and self-tests), the window is 23 to 90 days after exposure.

The CDC recommends that, if you receive a negative result from your first test, you should wait after the window period for the testing method you used before testing again. If you’re still negative after the second test and you had any other potential exposures, you’re HIV-negative. If you’ve possibly been exposed to HIV again, it is best to test again after the window period for that exposure.

If Your Partner Tests HIV-Negative, Are You Safe?

Even if your partner has a negative test result after an exposure, it doesn’t mean your test result will also be negative. Recommendations state that each partner should have their own HIV testing done to confirm their results. HIV is different for every person, and the length of time it takes for it to become detectable with a test can vary between individuals. It’s best to be open and honest with your partner about potential exposures and that both of you get tested.

Precautions To Take After Testing Negative

There are certain steps you can take after testing negative to help ensure you remain HIV-negative during the window period. These can also be done if you or your partner has had an exposure after an initial negative test. These steps include choosing less risky behaviors to lower your chances of exposure and taking preexposure prophylaxis (PrEP) or postexposure prophylaxis (PEP).

Choose Less Risky Behaviors

Because having unprotected sex is the most common way of spreading HIV, you and your partner can take extra caution to prevent potential exposure. If you or your partner has had an exposure after testing negative for HIV, you may not know whether the virus can be spread. Exercising caution by using condoms, choosing different sexual encounters/activities, or not having sex can help prevent spreading HIV.

Using condoms helps prevent the exchange of bodily fluids, stopping them from coming into contact with the mucous membranes in the anus or vagina. Condoms can also help prevent the spread of other sexually transmitted infections (STIs), such as chlamydia and gonorrhea. To reduce the spread of HIV effectively, it's important to use condoms regularly — including every time someone has been exposed to the virus.

The type of sexual activity also affects the risk of spreading HIV. The risk of spreading HIV from one person to another is highest in anal sex because the lining of the rectum (the last part of the large intestine) is thin. It is particularly risky when the HIV-positive person is inserting their penis into the anus of a person who is HIV-negative.

Vaginal sex carries less of a risk, but it is still possible for any participant to get HIV from it, regardless of their sex.

Engaging in oral sex (whether receiving or giving) or sexual behaviors that don’t involve the exchange of bodily fluids carries the least amount of risk. While it may still be possible to contract HIV from these exposures, it is much less common.

Reduce Your Risks With Preexposure Prophylaxis

Preexposure prophylaxis is a medication used to prevent HIV infection in people who are at a higher risk of contracting the virus. It reduces the risk of getting HIV through sexual intercourse by 99 percent and through shared needles by 74 percent.

PrEP is recommended for those who:

• Have vaginal or anal sex and have an HIV-positive partner
• Have been diagnosed with an STI within the last half year
• Do not use condoms every time they have sex

Pregnant people who have a partner with HIV may also use PrEP to help prevent the spread of HIV to themselves and the fetus during pregnancy and while breastfeeding.

Prevent HIV Infection With Postexposure Prophylaxis

If you think you’ve been exposed to HIV, talk to your doctor or health care provider as soon as possible within three days of the exposure. They can help you get postexposure prophylaxis, or medications that can be taken soon after an exposure to prevent the virus from infecting you.

The earlier you can begin PEP, the better the chances of preventing an HIV infection. The medications are taken every day for 28 days, and then your doctor will have you tested again to determine whether they worked.

Living With a Serodiscordant Relationship

A serodiscordant (HIV-discordant) relationship refers to a relationship in which there is one HIV-positive partner and one HIV-negative partner. If you or your partner tests positive for HIV, there are certain recommendations for ensuring the negative partner remains HIV-negative.

For the HIV-negative person, this includes consistent testing and taking PrEP, while the HIV-positive partner should take antiretroviral therapy (ART). These medications are used to prevent the virus from creating more copies of itself, which increases the viral load (the number of virus copies found in the blood).

The goal of taking ART is to eventually have an undetectable viral load. This means that your copies of the virus are so low that the viral load test cannot find them. When people with HIV maintain a consistent undetectable viral load by taking ART, there is considered to be no real risk of infecting an HIV-negative person by having sex, and PrEP may no longer be needed.

Keep in mind that if you or your partner had an exposure and received a negative test result, it is still possible to spread the virus if the testing was done too early and missed the infection. If you have certain risk factors, you may want to get tested at least once a year.

Talk With Others Who Understand

On myHIVteam, the online social network for people with HIV, more than 40,000 members come together to ask questions, give advice, and share their stories with others who understand life with HIV.

Have you or a loved one been diagnosed with HIV? What steps do you take to keep yourself or your partner safe? Share your insights in the comments below, or start a conversation by posting to your Activities feed.