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passing resistant virus pospos
Feb 21, 2005

What is the likelihood of a positive man who is resistant to one or more classe of drugs passing on resistant virus to another positive man through unprotected anal intercourse? Can you refer me to research in this area?

Response from Dr. Sherer

I would suggest that you go to the CDC website ( and look at the information on HIV risk reduction and the risk of transmission associated with various risk behaviors. Many other sources, including this website, also discuss this information.

There is little information comparing the risk of transmission of drug resistant variants to wild type virus. In the absence of this more specific information, you should regard the risk of transmission of resistant virus to be the same as for wild type. Among sexual practices, unprotected receptive anal intercourse carries the highest risk sexual transmission. There have been estimates made of the likelihood of such events, e.g. 1 transmission per 10-100 encounters, but these are only estimates. Other factors affect the risk of transmission, such as the presence of an untreated STD; lack of circumcision; and the degree of viral load elevation in the HIV positive person. There is evidence that the higher the viral load in the index patient, the higher the risk of tranmission. The story is more complicated than that, as the evolution of the virus differs in the plasma and in genital secretions. People with viral loads below detection are at a decreased risk of transmission, but there are documented instances of transmission even in the presence of plasma viral loads below 50 copies/ml.

For all these reasons, physicians continue to advise safe sex practices for people living with HIV, including those on ART with good outcomes. I would urge you to talk to your doctor about these issues as well.

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