Treatment News

Compiled by Gus Cairns

Resistance rates tumble – but there may be more there than meets the eye

The Retrovirus Conference heard good news on HIV drug resistance. Rates of resistance are falling, both in terms of the proportion of patients who catch drug-resistant HIV, and the proportion who develop it on treatment.

However another series of studies found that by using ultra-sensitive resistance tests, doctors could detect more resistance than by using standard tests – and that this resistance often caused HIV treatment failure.

A study from British Columbia in Canada found that the number of patients on HIV treatment who developed resistance had tumbled from 500 cases in 1996, through 200 cases in 2002, to only 80 cases in 2007. The proportion of patients achieving an undetectable viral load went up from 65% in 2000 to 86% in 2007.

And a study of French patients with recent HIV infection found that the proportion who caught HIV that was drug-resistant had peaked at one in six in 2000-2003 but in recent years had declined to one in nine. In the UK the results are even better with only one in 12 patients catching resistant virus.

However this isn’t the rule everywhere: a study from California found that the proportion had stayed stayed at about one in eight.

Meanwhile a study using ultrasensitive resistance tests that can pick out as little as one resistant virus in 3000 non-resistant ones found that there is a lot of hidden resistance around; it picked out over twice as many patients with some degree of drug resistance as standard tests could find. This resistance mattered, too: patients with resistance detected by the standard test were over six times more likely to fail their therapy than non-resistant patients, but patients with even tiny amounts of resistance detected by the ultrasensitive test were still 3.5 times as likely to fail.

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