Human immunodeficiency virus (HIV) is a viral infection spread through sexual contact or exposure to bodily fluids such as blood and breast milk. If you and your partner are HIV-negative and have been properly tested, with no recent exposure, it is not possible to contract HIV. However, if you or your partner has had an exposure but tested negative, it may still be possible to spread the virus to others if 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.
The first step in HIV prevention is understanding how the virus spreads. It can only be spread through contact with a person who has HIV by exposure to their bodily fluids (blood, semen, vaginal or rectal fluids, or breast milk). Possible exposure may occur through anal or vaginal sex, or sharing needles or syringes with an HIV-positive person. 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 mother to the fetus.
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.
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.
One test that does not depend on the immune system to build a response is the nucleic acid test for HIV, which detects the actual genetic material (RNA) of the virus. However, this test is not considered reliable until about 10 days after exposure because it takes that long for the virus to reproduce enough that the test can find it in the blood. Finally, 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 from the body 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.
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 the following:
If you receive a negative result from your first test, the CDC recommends waiting until after the window period for the testing method you used before you test again. If you are still negative after the second test and you haven’t had any other potential exposures, you are HIV-negative. If you may have been exposed to HIV again, it is best to test again after the window period for that exposure.
Yes — even if you have a negative test result after an exposure, it doesn’t mean your partner’s test result will also be negative. Recommendations state that your 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. Because HIV can be transmitted in ways other than vaginal or anal sex, it’s best to be open and honest with your partner about potential exposures and both get tested.
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).
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 its spread.
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.
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 both men and women to get HIV from it. Oral sex or sexual behaviors that don’t involve the exchange of bodily fluids carry the least amount of risk. While it may still be possible to contract HIV from these exposures, it is much less common.
Pre-exposure prophylaxis is a medication used to prevent HIV infection in people who are at a higher risk of contracting the virus. It is 99 percent effective when used correctly. PrEP is recommended for those who:
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.
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.
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 takes 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.
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