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How much “PrEP-resistant” HIV is out there?
Gus Cairns, 2018-03-09 13:20

A study presented at the recent CROI 2018 conference aims to quantify how many people with HIV there might be in the community who both have a detectable HIV viral load and also have significant resistance to tenofovir and emtricitabine, the two drugs currently used in pre-exposure prophylaxis (PrEP).

The researchers, from the University of Washington in Seattle, found that in King County, which contains Seattle, no more than 0.3% of the local HIV-positive population had viral loads over 10,000 copies/ml, and also high-level resistance to tenofovir and emtricitabine.

However an even smaller proportion of newly diagnosed people – just three cases in ten years, or one in 606 of those diagnosed – had primary drug resistance, i.e. actually became infected with tenofovir/emtricitabine-resistant HIV, and this is more likely to reflect the maximum frequency of people who could acquire drug-resistant HIV from someone else despite being on PrEP.

Most of the people with PrEP-drug resistance were long-term diagnosed people over 50 who might no longer be so sexually active on average. In addition, much of the drug resistance is likely to be “archived resistance”, i.e. present at the time they were tested, but possibly not a significant proportion of their viral load now. This is because tenofovir-resistant HIV is less fit than non-resistant HIV and may stop being a significant part of someone’s viral population over time.