Low or Undetectable Viral Low: Lower Chance of Transmission?
Answered by Oliver Bacon, MD, HIV InSite Medical Editor
Question
I have met a guy who just told me that he has HIV positive after the night we messed around, and he said that he has a low viral load and I shouldn't be concerned about getting infected. I gave him oral and there was precum. He also gave anal but it didn't really go all the way. Now I am worried that I may have been exposed now after that night. Is it true that I have a very low chance of getting it since he had a low viral load count?
Answer
I'm sorry to hear that you are going through this. Yours is a difficult question to answer, because no study has examined this question directly (there is a large, multi-country study of this subject underway, but we won't know the results for a long time -- several years at least). Nevertheless, many people have started assuming that a low viral load means a low risk of transmitting HIV. This is a tricky assumption. Here are some possible answers to your situation, none of them a sure thing:
1. If he is not taking antiretroviral therapy and his viral load (the amount of HIV measured in his blood) is still very low (less than 1,500 copies per mL of blood), then it appears that his likelihood of infecting you is low. This is based on a study of Ugandan couples, none of whom were taking antiretroviral therapy, in which one partner was HIV positive and the other was HIV negative. When the HIV positive partner's viral load was lower than 1,500 copies/mL, transmission to the HIV negative partner was not observed.
2. If his viral load is low because he is taking antiretroviral therapy, then it's difficult to know his risk of infecting you. While most studies show that antiretroviral therapy suppresses viral load in both the blood and in semen, some other studies show that people can still have a detectable (and even high) viral load in their semen or vaginal secretions despite having an undetectable viral load in their blood.
3. Also, just because his viral load was low last time it was checked, doesn't necessarily mean it was low when you had sex with him; other infections, especially sexually transmitted infections such as syphilis, gonorrhea, and chlamydia, can temporarily raise someone's viral load.
So it's hard to say what your risk from this encounter was. If it's been within 72 hours since you had sex with him, I would strongly encourage you to seek PEP (postexposure prophylaxis, or one month of combination antiretroviral therapy) as soon as possible. In any case, getting tested now, in one month, and in three months is a good idea, as is wearing a condom during sex.
Best of luck.
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