Experts said the study, the largest of its kind ever conducted, showed the need for patients to adhere strictly to drug regimens and to avoid spreading the disease.
The study, presented by scientists at the University of Utrecht in the Netherlands at an international conference, involved 1,633 HIV patients from 17 European countries diagnosed between 1996 and 2000.
It found that 9.6 percent of newly diagnosed HIV patients in Europe are infected with a virus that is resistant to at least one drug. About 2 percent had an infection that does not respond to two or more types of AIDS drugs.
Dr. Peter Piot, executive director of UNAIDS, said the findings are the most reliable to date.
A smaller study in San Francisco had found that 27 percent of 225 patients had drug resistant HIV strains.
But it was the larger European study that concerned researchers.
“You’re not talking about high-risk inner city San Francisco, this is across Europe,” the study’s co-author Dr. Charles Bouchertold told the New York Times.
Patients infected with HIV subtype B, the strain of the virus that is found in over half of infected Europeans and North Americans, were four times more likely to get a resistant infection than those who contracted other varieties of HIV, said study co-author David van de Vijver.
HIV subtype B is more likely to be drug resistant because medicine to fight that strain has been in use longer. The longer time period has given the virus more time to develop resistance, study researchers told the BBC.
Scientists found that non-adherence to drug treatments is likely the main reason for the emergence of drug resistance. But van de Vijver said he worried that the spread in Europe also suggested many people on treatment were returning to high-risk behavior, such as engaging in unprotected sex and sharing hypodermic needles.
Joep Lange, president of the International AIDS Society, said drug resistance is inevitable because HIV mutates swiftly.
“That means we need to develop new drugs all the time and that also means that we need to keep research-based [pharmaceuticals companies] interested in HIV because if they are not interested any longer there will be a point of time when we are in a desperate situation,” he said.
Lange rejected as “totally ridiculous” suggestions that the risk of resistance was a reason not to supply antiretrovirals to the developing world, where drug supplies and medical care may be less reliable.
Piot said the extent of resistance serves as a warning that the delivery of drugs in poor countries needs to be carefully controlled.
“It reminds us that when we introduce antiretroviral therapy we’ve got to do it well,” he said, adding that a universally followed standard prescription for initial treatment should be part of the strategy.
Currently, there are almost 20 separate anti-HIV drugs on the market, falling into three main classes: nucleoside reverse transcriptase inhibitors, non-nucleoside reverse transcriptase inhibitors and protease inhibitors.
Van de Vijver reported that 6.9 percent of patients studied had HIV that was resistant to the first class of drugs, 2.6 percent to the second class, and 2.2 percent to the third class.
Researchers and pharmaceutical companies are working to develop a range of new medicines to attack the virus in novel ways.
These include several drugs designed to block HIV’s entry into healthy cells. The pharmaceutical firms Roche and Trimeris recently introduced the first of these drugs, a so-called fusion inhibitor called Fuzeon, in Europe and the United States.
Other companies are working on so-called integrase inhibitors, designed to block another step in the life cycle of HIV, although these are only at an early stage of development.