Mutant HIV in San Francisco Men Resists Drugs; Researchers Say New Viral Strains Adapting Quickly

Mutant strains of HIV resistant to many of the newest drugs are turning up in larger numbers of newly infected gay men in San Francisco, according to a five-year study released at the 14th International AIDS Conference. The findings are based on a University of California-San Francisco study of genetic changes in HIV blood samples of patients known to be infected within one year of the test.

Findings of the study include:

• In 1996, only 2.5 percent of those tested for HIV were infected by a virus resistant to two different classes of drugs. That number rose to 13 percent by 2000. Resistance had developed quickly to the newest class of AIDS drugs, non-nucleoside reverse transcriptase inhibitors.

• The mutated viruses are being spread by patients currently under treatment, in whom the virus is evolving ways to sidestep medicines targeted against it.

Dr. Frederick Hecht, co-author of the study released early for the conference ("Time Trends in Primary HIV-1 Drug Resistance Among Recently Infected Persons," Journal of the American Medical Association, 2002; 288:169-180) said the research is important because patterns detected among the city's closely studied populations of HIV-infected men are early indicators of how the epidemic will evolve elsewhere.

It remains unclear, however, just how dangerous the trend may be. The number of patients initially infected by the drug-resistant strains remains small, and there is some evidence that mutant viruses are less lethal than their wild-type counterparts.

Patients initially infected with the newer viral strains showed a higher level of disease-fighting white blood cells than those carrying the non-mutant virus. In theory, the mutant strains may be so battered by antiviral drugs that they are evolving into a less dangerous virus. Hecht cautioned, however, that the differences in blood cell counts were not large and further studies are needed to determine whether the new viruses are "less fit" to do damage. It can take 10 years for an untreated HIV infection to progress to AIDS.

In the short term, a new infection by a mutant strain is more problematic to treat because patients with the new virus must start their treatment with drugs of last resort, the "salvage regimes" normally reserved for those who have failed prior treatments.

Back to other CDC news for July 8, 2002

Previous Updates