Q and A


Is PEP effective if taken 48 hours after exposure?

I paid for sex with a woman but the condom tore and I only realised after I was done. There is a high chance that she was HIV positive. I started PEP after 48 hours.

I got a PCR test done 17 days after exposure. It had a less than 20/ml (undetectable) result.

Now between 14 and 35 days after exposure I have had signs of thrush, mild red rash on my face and a couple elsewhere. But no fever or swollen lymph glands.

Can the rash and thrush be because of utter stress and obsession?

My doctor says that the PCR can be relied upon and that I am negative.

Can the PEP have reduced the viral load to less than 20/ml as I took it for 15 days before the PCR test?

Please give your expert advice. I am very anxious. Thank you.


Thank you for your question.

The risk of HIV from one broken condom is very low. If your partner had an undetectable viral load on treatment, then the risk would be zero. If they were not on treatment the risk might still be only 1 in 300 or lower.

You cannot guess someones HIV status so your assumptions might also be wrong.

You started PEP within 48 hours, so it is likely it will work.

PEP – stands for Post-Exposure Prophylaxis. It is a term used for taking HIV drugs to reduce the risk of infection. PEP usually involves taking a combination of three HIV drugs for one month. The earlier PEP is started, the more likely it will work. Ideally, this should be within a couple of hours. If this is not possible, then still the earlier the better.

Some guidelines include a two-day window to do this (i.e. within 48 hours). After this, effectiveness is much less likely. Other guidelines allow up to 4 days (i.e. within 72 hours). Sometimes this may be more for psychological benefit. For example, if someone is very stressed or traumatised.

No guidelines recommend starting PEP after 72 hours.

After finishing PEP you need to wait a 4-6 weeks before testing.

If the PEP has worked, or the person was not initially infected, this will show as a negative HIV test. The test you did 17 days after the exposure will not be accurate yet.

If the PEP has not worked, this will be shown in a positive test result. Testing 4 weeks after PEP will detect 95% of infections. Testing after six weeks will detect more than 99% of infections. This result doesn’t need to be tested again.

If PEP has not worked, serosonversion usually occurs 1-3 weeks after PEP is finished. However, only 80% of people show symptoms.

Please test 6 weeks after you finished PEP is finished. If you test any earlier, you need to take a second test 3 months later.

Viral load (PRC) tests are not approved to test for HIV. In some cases they can have a role.

Please see a doctor to talk about your symptoms he best way to confirm what is causing them is to see your doctor. He/she will be able to diagnose and treat the symptoms accordingly.

Note: This answer was last updated in July 2021 from an original post from December 2011.


  1. Lisa Thorley

    Hi Likius,

    As the post states, PEP should be taken within max 72 hours after a possible exposure.

  2. Likius

    Is 69 hours fine to start pep?

  3. Simon Collins

    Dear Tumi, please see links here for online info about risk.

  4. Tumi

    Hi can I get infected with HIV if the sexual body fluid touched a small cut on my fingers.

  5. Lisa Thorley

    Hi Liam,

    As the potential risk was less than 72hrs ago and you’re not sure if this guys is positive or not, the best thing to do (for your own piece of mind) is to take a course of PEP.

  6. Liam

    I have had condomless sex with a guy I was receptive and he said he was on prep but he blocked me should I trust him or should I get pep because it is coming up to 72 hours tomorrow

  7. Lisa Thorley

    Hi Aba,

    For PEP to be effective it needs to be taken within max 72hrs. As you started after 6 days it won’t work.
    You’re going to need to test, please see Q 1 here: https://i-base.info/qa/what-are-the-most-asked-questions

    So as to ensure that you don’t put yourself at risk again, you might want to think about using condoms. Though HIV is now a very treatable condition, if you have sex with someone who is positive and not on medication you’re putting your health at risk.

  8. Aba

    Am Aba
    I had unprotected sex with a lady which is HIV positive and she isn’t on treatment.after 5 days I checked her and find out her status when she’s positive.the following day we went to the hospital and find out her status when she’s positive and mine wz still negative and I started taking PEP on 6th day after the exposure and now it’s 11 days on PEP but I don’t have much side effects other than body itching and little sweating at night.what are the chances of me getting infected after finishing up all my course of PEP medicines without fail,, please please am scared,, I need your answers

  9. Simon Collins

    Info about transmission, testing and PEP is available from the links at this Q:
    You partner’s viral load is already likely to be much lower after ebing on ART for 4 weeks.


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