By Daniel Haney

AP 8 February 2001

Chicago People who catch HIV are increasingly likely to encounter mutant forms of the virus that are able to resist some of the drugs commonly used to treat the infection.

Drug-resistant strains have been a major problem since the start of treatment in the early years of the AIDS epidemic, but until recently this resistance emerged as the virus evolved inside each patient's body. Now, however, doctors say these resistant viruses apparently are being passed on to others in significant numbers.

U.S. researchers Wednesday reported an abrupt upswing over the past two years in the prevalence of resistant forms of the virus in newly infected people.

They said the cause of this increase is almost certainly the widespread use of drug combinations that have revolutionized the treatment of AIDS since 1996. These medicines have transformed HIV from a death sentence to a manageable condition, but they have also increased the number of outwardly healthy people whose bodies harbor resistant virus.

When all goes well, the drugs hold reproduction of the virus so low that no resistant mutants can evolve. But often, the medicines fail to work this well, and a virus gradually emerges that is resistant to one or more of the drugs being taken.

"There are significantly greater numbers of patients who have failing regimens and who transmit their virus," said Dr. Susan Little of the University of California at San Diego.

Her study was conducted on 394 people in Dallas, Denver, Los Angeles, San Diego, Montreal, Birmingham, Ala., and Vancouver, British Columbia. She presented the results at the Eighth Annual Retrovirus Conference in Chicago.

The patients were seen by doctors between 1995 and last May. All were checked within three months of catching HIV.

Between 1995 and 1998, less than 4 percent of the patients caught resistant virus. In 1999 and 2000, this rose to 14 percent. Six percent of these had a virus that was resistant to two drugs.

Most of those who catch HIV never realize it until years later. However, patients occasionally realize it soon after infection because they get temporary flu-like symptoms. Some doctors recommend immediate drug treatment for such patients.

In these cases, Little said doctors should check their patients' viruses to see if they are resistant to any drugs before starting therapy.

Doctors believe that without treatment, patients' drug-resistant virus eventually evolves back to the non-resistant form. However, a record of the resistant virus is stored in patients' immune systems, and it can re-emerge once treatment starts.

The growing spread of resistant virus "has tremendous important in our ability to treat people effectively," said Dr. Douglas Richman, another member of Little's team.

Another study, conducted by Dr. Hillard Weinstock of the Centers for Disease Control and Prevention in Atlanta, raises the possibility that the level of resistant virus varies greatly among different risk groups.

Weinstock's team surveyed 603 people newly diagnosed with HIV in 10 cities. It found that 16 percent of white homosexual men had resistant virus, compared with 3 percent of blacks who caught the virus heterosexually.

Two other studies from Switzerland and France also found high levels of resistant virus, though resistance was more common there than in the United States during the mid-1990s. In a study of 121 newly infected patients, Dr. Marie-Laure Chaix of Necker Hospital in Paris found that 9 percent had resistant virus in 1996, 7 percent in 1997, 6 percent in 1998 and 10 percent in 1999.