Resistance develops when patients take their HIV drugs irregularly. Credit: © GettyImages

One in ten people who test positive for HIV in Europe is infected with a virus that is already resistant to drugs, suggests a Europe-wide survey.

Europe's resistance levels are now akin to those in the United States. "This limits the number of drugs available to treat these patients from the beginning," says Joep Lange, director of the International Antiviral Therapy Evaluation Centre in Amsterdam, Holland.

Resistance develops when patients take their HIV drugs irregularly, allowing the virus to survive and adapt. Resistant viruses are thought to be less infectious, but they can be passed on to some extent. "It could have been predicted," says Lange.

Researchers from 19 European countries tested 1,633 newly infected patients for mutations linked to resistance in the HIV virus. They presented their findings at this week's International AIDS Society meeting in Paris.

The study highlights serious problems in the management of anti-HIV drug use, says virologist Richard Tedder of University College London. Too many patients do not or cannot comply with their treatment regimen, or are being prescribed drugs to which they are likely to become resistant, he reckons. "Some clinics are breeding grounds for new resistance," he says.

Some clinics are breeding grounds for new resistance Richard Tedder , University College London

But the results could be an overestimate, Tedder adds. HIV mutates so rapidly that people are infected with a "swarm" of different varieties, he says. This makes it difficult to know whether a resistance mutation that shows up in a test will actually cause problems once the patient begins drug treatment.

Experts at the meeting called for new ideas on how to manage resistance. "The single most important factor is adherence to drug therapy," says HIV-resistance specialist Deenan Pillay, also of University College London.

Efforts are being made to combine unwieldy multi-drug regimens into a single pill that can be taken just once a day. Patients who are most likely to harbour and transmit resistant forms of the virus should also be counselled on how to minimize the risk, Pillay says. "Resistance shows that there is failure of all the messages we are putting out."