I'm HIV negative and practice safer sex, but since HIV is a fact of life in the gay community in which I life, I try to stay educated on the prevention and treatment of HIV.

I have two questions about drug resistance. If I were to acquire HIV from someone who was on HIV meds, however unlikely, as the virus begins to replicate in my body without the HIV meds will it become resistant to the HIV meds the person who transmitted it to me was taking?

Secondly, is it common for HIV resistant strains to be transmitted? There's a lot of comfort in knowing that HIV can be treated as a chronic condition with a near normal life span using a simple once-a-day drug regimen. However, is it common or is there a high risk of acquiring a strain of HIV where there is a poor prognosis due to limited treatment options at the time of diagnosis?

To take your second question first, yes, it is common for resistant HIV to be transmitted. In this era in the United States, about 10% of people acquire a strain of HIV that carries one or more drug resistance mutations. In some cases, the people that they acquire the virus from are on medications and have developed resistance to some ART medications; in other cases, the individuals from whom they acquired the virus have never been treated with ART, but they themselves have acquired a virus with drug resistance mutations from someone else.

Forunately, the frequency of the transmission of multi-drug resistant virus is very low. In most series looking at genotypes performed in newly diagnosed patients who have never been on ART, only 2% or few patients have resistance to two or more drug classes, and transmission of virus with complete resistance to all drugs is quite rare.

And, in general, the presence of transmitted resistance has not impeded the ability of an HIV physician to find a regimen to which their patient is fully susceptible. In some cases, transmitted resistance may limit the treatment choices, but this usually can be overcome with the right choice of initial ART. For this reason, HIV clinicians perform a genotypic resistance test in all patients with HIV before they start ART, so that they can avoid the use of drugs to which the patient is likely to have a less than optimal response.

It is useful to know that the virus pays a price for each resistance mutation, in terms of the replication capacity of the virus, i.e. its ability to replicate, and in terms of the overall fitness of the virus. This is why, again in general, when a person with a virus with multiple mutations stops all ART, the resistant virus tends to be overgown by wild type virus in a short period of time, which is more 'fit' in comparison to the resistant virus. If a doctor performed a resistance test at such a time, it might sugggest that the patient's virus is fully susceptible to all drugs, because the majority population in the viral swarm is wild type. However, that would be misleading information, because the resistant virus is still present, though at low levels that might be missed by a standard resistant test. We refer to this phenomenon as 'archived resistance', and it is one of the compelling reasons that HIV physicians need to have a patient's full treatment record, including responses, of all past ART regimens, when he or she is interpreting a drug resistant test. If that same patient was started back on ART, the same resistant viral strains would quickly become the dominant strain, and the patient would again fail the regimen due to the re-emergence of the viral strains with 'archived' resistance mutations.

As to your first question, if you acquire a wild type virus with no mutations, and you are not on ART, then you are not at risk for developing a drug resistant virus. Only the pressure of active ART leads to the development of drug resistance.

I encourage you to talk to your doctor about your questions and these responses.