Drug-resistant strains of HIV, the AIDS virus, have spread widely since the first effective drugs were introduced five years ago, making the deadly disease far tougher to treat, researchers reported Tuesday in the first large-scale study of the extent of HIV resistance.
The study, which focused on patients treated between 1996 and 1999, found that 78% harbored virus that was resistant to one class of drugs, 51% had virus that was resistant to two classes of drugs, and 18% had virus that was resistant to all three classes of drugs.
"The prevalence of resistance is much higher than we thought," says lead author Douglas Richman of the VA San Diego Healthcare System.
The ease with which HIV changes to protect itself against the most lethal drugs available represents evolution in action. Only the fittest viruses survive to multiply, quickly filling the void left by their more vulnerable ancestors. Moreover, the more resistant HIV there is, the more it will spread from person to person, Richman says. "I think this indicates why we're seeing much more transmission of drug-resistant virus."
Prior studies have shown that 10% to 20% of people newly infected with HIV carry drug-resistant strains.
The new study relied on blood samples taken from 1,083 patients who were no longer benefiting as much from their treatment. This population was statistically representative of 132,442 people treated between 1996 and 1999, says Richman, who collaborated with experts at the Rand Corp.
Jose Zuniga, director of the International Association of Physicians in AIDS Care, says doctors should test their HIV patients for drug-resistant virus after the drugs' benefits fade, so they can tailor therapy to the patient.
This isn't a simple matter, because current resistance tests measure resistance only in the most common AIDS strains. Resistance in up to half of the less common strains may be missed, and the results can be difficult to interpret. Zuniga notes that newer, better tests are in the works.
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, called the study's results "striking," but he said that better tests are only part of the solution. "This is a wake-up call to develop new drugs."
Researchers say studies have shown that the $400 to $1,000 tests are cost-effective, because they spare patients costly treatment with ineffective drugs and keep them out of the hospital. One study, done in France, found that treatment failure adds $250 to the monthly cost of a patient's care.
The research also has implications for treatment in poor nations. These countries, now able to purchase discounted or generic versions of AIDS drugs, could experience the rampant spread of drug-resistant virus unless doctors prescribe the drugs properly and patients comply with their doctor's orders.
Otherwise, Zuniga says, the drugs will lose their potency and HIV will again become untreatable.
Richman presented his results in Chicago at the Interscience Conference on Antimicrobial Agents and Chemotherapy. He is a medical director of ViroLogic Inc. of South San Francisco, which makes the test used in the trial.
