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WASHINGTON: More than three-quarter of all US patients with the AIDS virus have an infection that resists one or more of the drugs used to treat it, researchers have reported.
They said the grim news meant that drug-resistant HIV had spread even faster than was feared, and the lifesaving cocktails of drugs that help many patients lead normal lives were becoming increasingly limited in their usefulness.
Unless better drugs are developed soon, or until a vaccine is invented that can control the virus, patients will have ever-lessening chances of using drugs to counter AIDS, the researchers told a conference sponsored by the American Society of Microbiology.
Some already have no chance at all, Dr. Douglas Richman of the Veteran's Administration hospital and the University of California in San Diego, who led the study, said.
"A number of these patients are not readily treatable," Richman said in a telephone interview.
Richman and colleagues tested blood samples taken in 1999 from 1,647 men and women. They used a test made by South San Francisco based ViroLogic Inc. to test how the virus responded to the many available drugs used to test HIV.
"They reflect almost 209,000 people and about 130,000 who have detectable viremia (levels of virus in the blood)," Richman said.
Of these, Richman's team told the Interscience Conference on Antimicrobial Agents and Chemotherapy in Chicago, 78 per cent carried virus that resisted at least one drug. "Just over 50 per cent of them were resistant to more than one class of drugs," Richman said.
Other studies had shown that HIV was evolving to evade nearly every drug available, but these are the most startling numbers yet.
"Many of the previous studies were relatively small and in highly selected populations, so that accurate estimates were not possible," Dr. Samuel Bozette, who worked on the study, said in a statement.
Bacteria are known to mutate to resist drugs, which is why new anti biotics are being developed regularly.
But Richman said a virus such as HIV is trickier than any bacteria. "The reason is this virus replicates to higher levels at faster rates, so it evolves faster," he said.
"Once resistance is there, it stays in a patient for the rest of his or her life. You don't get cured of an HIV species."
With bacteria, it is often possible to take a patient off antibiotics and socalled wild-type bacteria will eventually move in and push out the drug-resistant versions. Not so with HIV, which lurks in the body for decades, perhaps forever.
HIV has no cure and is always fatal, but mixes of drugs, known as highly active antiretroviral therapy (HAART) can keep patients alive and living near normal lives for years.
There are four classes of these drugs available, each of which attacks HIV at a different point, and a mixture is required to make it work. The timing and composition of this cocktail is an art for AIDS doctors.
Richman said the study showed that doctors will have to start testing their patients right away to see if they have been infected with a resistant version of HIV.
"We have to use drugs more intelligently. This is the responsibility of physician and patient," he said. "We have to try to figure out ways to prevent transmission ... and we have to find drugs to work against resistant virus."
Preventing transmission is also difficult. Reassured by news about the success of HAART over the years, many people see HIV as a treatable illness and are indulging in risky behavior such as having unprotected sex, researchers have said.
They are ignoring advice to use condoms, despite reports in recent years that as many Americans are getting HIV as ever before and warnings that the drugs would not work forever.
"We identify two to three new (HIV) patients every week and if anything, things are getting worse," Richman said.
About 40,000 people are infected with HIV every year in the United States, with half the cases in people under 25.- Reuters