CNN HEALTH Special Section

LOS ANGELES (CNN) -- News from the 12th World AIDS Conference in Geneva that a San Francisco man has contracted a multi-drug resistant strain of the AIDS virus is sobering to communities such as West Hollywood, California.

"It seems we are going right back to the beginning of the AIDS crisis," said one resident.

The San Francisco man caught the virus last fall from someone who had taken many drugs, including protease inhibitors, on and off for several years. The man's HIV is resistant to four different protease inhibitors and the drugs AZT and 3TC.

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"It selects the virus to try and escape from the drugs by becoming resistant," said Dr. Anthony Fauci of the National Institutes of Health. "That's a natural thing that any microbe does when you treat it."

Bound to happen

Some experts in the field of HIV disease treatment said the report of a resistant HIV strain is not unexpected.

"Upwards of 5 percent of the people coming in that are intitally positive are already resistant to AZT," said Dr. Scott Hill of the President's AIDS Advisory Council. "So it shouldn't be surprising that we're going to see multi-drug resistant strains."

Patients infected with HIV who fail to take protease inhibitors precisely as prescribed can allow mutant viruses to develop that are resistant to the very drugs that revolutionized AIDS treatment.

"We had this honeymoon where the medications were working wonderfully, and now some people are becoming resistant," said Eddy Garcia-Fernandez of the AIDS Project Los Angeles.

New drugs may offer hope

There are drugs available for newly infected patients who don't respond effectively to AZT, 3TC and other HIV drugs.

"Luckily, there are several choices of combinations of drugs, cocktails you might say, that will get somebody to non-detected," Hill said. "However, if they're resistant to different classes of drugs, we're in big trouble because there really are only a couple of classes of drugs right now."

Fauci said new drugs in development may be able to crack resistant strains.

"There are a whole new second and third generation of drugs that hopefully will not only be as powerful as the ones that we have now, but would also be getting around to this concept of cross-resistance," Fauci said. "In other words, if you have a resistant virus, new drugs might be able to overcome that resistance."

CNN Correspondent Jennifer Auther contributed to this report.