Drug resistant HIV in decline in UK
Posted by pozlife on May 21, 2007
The proportion of people with HIV who catch drug-resistant virus has definitely declined, in the UK, a new study confirms.
However it also shows that not enough resistance tests are being done: in the latest year for which we have data, 2004, only a sixth as many people had resistance tests done as were diagnosed that year, despite British HIV Association Treatment Guidelines saying that “testing for transmitted resistance continues to be recommended in all newly diagnosed patients”.
The study from the Collaborative Group on HIV Drug Resistance has found that transmitted drug resistance (i.e., not resistance acquired during treatment, but acquired through infection) declined, as a proportion of all infections, from around 14% in 2001-2 to about 8% by the end of 2004.
The study looked at 4,454 samples taken in resistance tests on patients who’d never taken HIV treatment between 1995, when the technology first became available, and the end of 2004.
It found that overall resistance declined from 14% to 8%, resistance to the nucleoside drugs (Truvada, Kivexa and the like) from a peak of around 9% in 200-02 to around 4.5% at the beginning of 2005, and resistance to protease inhibitors (Kaletra, atazanavir, etc) from 4% in 2001-2 to 2% in 2005.
The only bad news is that resistance to the non-nucleoside (NNRTI) drugs (efavirenz and nevirapine) did not decline so fast: resistance peaked at 5.5% in 2002-1 but only declined by a percentage point by 2005, meaning that NNRTI drug resistance is now as common as nucleoside resistance.
There had been signs that resistance was declining before, but surveys had only been done on individual patient groups such as those in Brighton. This is the first survey of what should be the vast majority of resistance tests done in the UK that shows a decline.
Resistance tests on recently-diagnosed people have become more routine. There were only 310 resistance tests done in 1996-7, and 519 in 2002. This had gone up to 1,185 in 2004, though this is still only 16% of the 7,536 infections diagnosed that year.
Some researchers have questioned whether the decline in resistance is real. They doubt it for three reasons.
Firstly, as resistance testing becomes more routine, it may naturally be extended to people who are less likely to be resistant. In the early days of resistance testing, for an (expensive) test to be ordered on a patient who hadn’t taken HIV drugs before, doctors would have to suspect they had resistance, for instance because the person who infected them was known to be resistant.
Secondly, the patients tested for resistance may have acquired HIV over a long span of time, from only a couple of months before the test to as long as ten years or so; so it’s difficult to tell if the decline in resistance is a recent phenomenon and if it’s still continuing.
Thirdly, the UK HIV epidemic has doubled in size since 2002, and the bulk of the increase has been amongst African immigrants who – because HIV drugs have till recently not been available in Africa – are less likely to have resistance.
However the resistance decline in this study looks real. Firstly, the researchers also looked at resistance in a subset of patients who had acquired HIV infection relatively recently: this means in people where there was evidence of a negative HIV test no more than 18 months before the date of the resistance test.
They found that resistance in these recently-infected people declined similarly, but that the decline started earlier: resistance peaked in 2000 at 12.5% and has declined more steeply to only about 4% now.
This is what you’d expect if the decline in resistance is genuine; it shows that the more recently people are infected, the less likely they are to have got resistant virus.
Secondly, in terms of the change in makeup of the UK HIV positive population, the proportion of resistance tests done on subtypes of HIV other than subtype B (which is the one passed on in the overwhelming majority of infections in the UK) increased from 8% in 1996-7 to 42% in 2004. But when non-B viruses were excluded from the study, the decline of resistance in ‘home-grown’ subtype B infections, though at a higher level, mirrored the decline in all infections.
Although this is good news, say the researchers, they add: “We caution against over-optimistic interpretation of our findings from a public health perspective.” They point out that although the proportion of HIV caught that’s resistant to at least one drug has nearly halved since 2002, the annual number of new infections has more than doubled, so there are a higher absolute number of people around with newly-acquired resistant virus.
However resistance may be continuing to decline. Amongst the subset of people with recently-acquired HIV infection tested in 2004, which numbered 50, researchers could only find two resistant samples – both with resistance to NNRTIs.