Dear Dr.Sherer,

what is the statistical likelihood of somebody getting infected by a Drug-resistant strain nowadays?If somebody is resistant to a class of drugs will the invidual he infects NECESSARILY be infected with the same drug resistant HIV? Thank you very much for your time.

The prevalence of drug resistance in the general population is quite variable, so you should be skeptical of any single number in answer to this question. In a CDC survey of chronically HIV-infected people who had never been treated previously in the US, 9% had resistance mutations to one or more drug, and 2% has resistance to 2 or more drugs. That is a reasonable number to use, unless there is better data available to you and your doctor.

It is reasonable to assume that if a virus is transmitted from a treated patient with resistance mutations, the same virus will be the one that is transmitted. However, it is not necessarily true, or rather it may not be true that the virus that such an individual transmits to another is always the same resistant strain. There can be a disconnect between the exact strains in the plasma and those in the genital secretions, i.e. the semen and seminal fluid in a man, and the vaginal and cervical secretions in a woman. That is why we speak of these sites as being 'sequestered sites' or 'protected sites'; there is not 100% uniformity between the swarm of virus in the bloodstream and the swarm of virus in these sites. The same is true for a 'disconnect' between the plasma and the central nervous system.

However, having said this, the majority of transmitted virus from a given individual will reflect the dominant species in the blood of the same individual, and will contain the same resistance mutations in the majority of cases.