More than 72 hours since a possible HIV exposure?

Missing the window for PEP (post-exposure prophylaxis) doesn’t mean you have HIV. Most single exposures carry a low chance of HIV in the first place. What matters now is getting tested at the right times so you get a clear answer.

What PEP can’t do now

PEP works by stopping HIV before it sets up a lasting infection. The longer the wait, the less it can do. The calculator assumes PEP lowers the risk by about 90% if started within 24 hours, but only by about 70% if started between 48 and 72 hours. CDC guidelines say the evidence is not enough to recommend starting PEP later than 72 hours.

Instead, the CDC recommends that people who come in after 72 hours get an HIV test, advice about PrEP (pre-exposure prophylaxis, medicine that prevents HIV), and a plan for follow-up testing.

Your risk is probably lower than you fear

Even with a partner who has HIV and isn’t on treatment, a single act of receptive vaginal sex carries an estimated 0.08% (about 1 in 1,200) chance of HIV, and receptive anal sex 1.4% (about 1 in 72). With a partner whose status you don’t know, the numbers are usually much lower. In the United States, for example, one act of receptive vaginal sex with a man of unknown status carries an estimated 0.00014% (about 1 in 730,000).

These are estimates, not a diagnosis. Only a test can tell you for sure.

Your testing plan

No test can detect HIV immediately after an exposure. Each type has a window period, the time between infection and when the test can pick it up.

A simple plan:

1. Now. An HIV test now shows whether you had HIV before this exposure. It can’t rule out an infection from the last few days.
2. From 45 days (about six and a half weeks). A lab antigen/antibody test (blood from a vein) is conclusive from 45 days after the exposure.
3. If you use a rapid or home test. A rapid antigen/antibody test (finger-prick) or an antibody test, which includes most rapid tests and home self-tests, is conclusive only at 90 days. Either retest then or get a lab test.
4. Earlier answer? A NAT (nucleic acid test) can detect HIV from about 10 days and is conclusive from 33 days. Ask your clinic whether they offer it.

A negative result taken inside the window is reassuring, but retest after the window to be sure. More detail is in the HIV window period and test accuracy by week.

Symptoms to watch for

Some people get a flu-like illness 2 to 4 weeks after getting HIV: fever, rash, sore throat, swollen glands or mouth ulcers. Many people have no symptoms at all. Symptoms can’t tell you whether you have HIV, because colds and other viruses look the same.

If you do get these symptoms in the weeks after an exposure, the CDC advises getting an HIV test. Tell the clinic when the exposure happened so they can choose the right test. See the HIV symptoms timeline.

While you wait

• Protect partners. Until you have a conclusive result, condoms lower the risk of passing HIV on by about 80%.
• Get checked for other STIs. They can be passed on at the same time, and many can be treated. See HIV and STIs.
• Look after yourself. Waiting for results is hard. If worry is taking over, read coping with HIV anxiety.

PrEP for the future

If this could happen again, PrEP can protect you before an exposure. Taken as prescribed, it lowers the risk of HIV by about 99% for anal sex and about 90% for vaginal sex. Options include daily pills and long-acting injections. You’ll need a negative HIV test before you start, so the testing plan above fits well. Read HIV risk on PrEP.

What to do now

1. Double-check the timing. If it might still be under 72 hours, go for PEP now.
2. Get a baseline HIV test and book a lab antigen/antibody test for 45 days after the exposure.
3. Act on symptoms. Fever, rash or sore throat in the next few weeks means it’s time to ask for a test.
4. Ask about PrEP if you may be exposed again.