A possible new strain of HIV (search) that is difficult to treat was isolated in a New York City man and is giving rise to the notion that a superbug is on the horizon. But many AIDS (search) experts view the idea with a skeptical eye.

Late last week, officials from the New York City Department of Health and Mental Hygiene announced a middle-aged man was infected with a new and unique strain of HIV -- one that resists most medications used to treat HIV and progresses to full-blown AIDS in a fraction of the usual time.

"Normally you don't see those two things together. Either a strain is drug resistant or it moves quickly, but not both," says HIV investigator Mary Klotman, MD, director of infectious diseases (search) at the Mount Sinai Medical Center in New York City.

"Virtually without exception, highly resistant viruses tend to be less destructive -- they can be destructive, but less destructive. You would not expect them to have a super-virulence," says Fred Valentine, MD, director of the AIDS Center for Research at the NYU School of Medicine.

New HIV Case a Wake-Up Call

In the case of the New York man, the virus has not responded to three of the four types of antiviral drugs used against HIV, and it progressed to AIDS in less than 20 months, just two months after a positive HIV diagnosis was made. Normally, progression from HIV to AIDS in an untreated patient takes 7 to 10 years, with death following months after that time.

The one drug this potential new strain is reported to respond to, Fuzeon (search), is most effective when used in combination with other antiviral drugs.

In a statement issued last Friday by New York City health officials, Commissioner Thomas R. Freiden, MD, MPH, called the discovery a “wake-up call” that should not be ignored. Indeed, the war on HIV is not only over, many experts believe the fight has not yet begun.

"I do think it's a wake-up call that public health measures are critical and that prevention is still the best mode of protection. The fact that you even have multi-drug resistant strains of this virus is a clear public health threat, with or without the superbug aspect," says Klotman.

The potentially new strain of HIV is known only as 3-DCR HIV (search). And New York health officials say it has been identified in only one patient. This initially led some researchers to theorize that the man's individual genetic susceptibility, not the virus itself, may be responsible for its rapid progression.

But this idea came into question on Monday when it was announced that two more cases could be on the horizon.

In New York City, officials announced another man may be harboring a similar strain of the virus, while in California, a San Diego man has tested positive for a similar infection. According to published reports, this man was diagnosed with HIV last fall, around the same time the New York City man was diagnosed, though there is no positive link between the two.

And while experts say more testing is needed to determine if all three viruses are really the same, New York City health officials have issued a nationwide alert for doctors and health departments to retest all patients recently diagnosed with HIV and to look for the new strains.

Is a Superbug Really Here?

Despite the frightening possibilities, many AIDS researchers remain skeptical that a superbug is in our midst.

"Right now there are two very basic questions that are not being answered publicly, and they are intrinsic to how frightening this story really is," says Valentine.

The first question: Is the New York City man infected by more than one strain of HIV?

The second question: Did his CD4 cell count (an indication of disease progression) ever respond to treatment, even for just a short while?

Why is this information critical? Valentine says it's not unheard of for one person to be infected with two strains of HIV: one a "wild" or unmutated strain that progresses rapidly but responds well to drugs, and a second "mutated" strain that replicates slowly but does not respond to treatment.

Although the "wild" strain becomes the basis for initial diagnosis, once treatment is started that virus recedes, allowing the mutated virus, which does not respond to drugs, to come forward. If medication is then stopped in response to the drug-resistant virus, the "wild," rapidly progressing strain moves forward again.

It is this back-and-forth motion, says Valentine, that can make it appear as if one superbug is at work when it's really the work of two separate strains.

"If at any point the New York patient had responded to drugs, there's good reason to believe this dual diagnosis holds the key to what we are seeing now, " says Valentine.

Two HIV Strains May Combine

In a slightly different scenario, Klotman says it's possible two different strains of the virus were contracted almost simultaneouslyfrom two different sources, and they landed in a single cell.

“It has been well documented in the past that when two strains infect a single cell they can recombine their genetic material and create a new and seemingly more powerful virus," says Klotman.

And indeed, both dual-infection theories are plausible since the New York City man admitted to not only being promiscuous, but also a heavy user of crystal methamphetamine, a street drug that lowers inhibitions and increases risky sexual behavior.

Says Valentine, “If it is really true that there is a superbug, a highly drug-resistant virus that is also replicating like gangbusters, then this is a very scary story. But based on the information released thus far, we cannot make that determination."

Both New York City health officials and experts from the Aaron Diamond AIDS Research Center, where 3DCR-HIV was originally isolated, did not respond to WebMD's requests for comments.

Ultimately, however, the one factor everyone seems to agree on is this: Even if 3DCR-HIV does not turn out to be the superbug we fear, it serves to remind us that the possibility of a more deadly strain of HIV could be around the bend.

By Colette Bouchez, reviewed by Brunilda Nazario, MD

SOURCES: Mary Klotman, MD, chief, division of infectious diseases, Mount Sinai School of Medicine, New York City. Fred Valentine, MD, professor of medicine; director, AIDS Research Center, NYU School of Medicine, New York City. News release, New York City Department of Health and Mental Hygiene. The New York Times, Feb. 13, 2005. Associated Press.