Fears of an AIDS superbug were alleviated Monday when researchers reported that they have homed in on the source of a New York City man's HIV infection.

Concerns had existed since February when officials from the New York City Department of Health and Mental Hygiene announced that a middle-aged man had purportedly been 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.

But viral testing shows that the man does not have a unique HIV strain, says Gary Blick, MD, medical and research director of Circle Medicine in Norwalk, Conn.

Rather, the New York City man has the same viral strain as an HIV-infected man in Connecticut, he says. The two men admit having unprotected sex with each other.

"The Connecticut patient's virus is a 99.5 percent match to the New York City man. They're essentially identical," Blick tells WebMD.

Speaking at a meeting of the International AIDS Society, Blick says that the 52-year-old Connecticut man infected the New York City man with a potent viral strain that is resistant to three of the four types of medications used to treat HIV.

Possible New Strain of HIV Investigated

Risky Behavior Blamed for Rapid Progression

One of the major reasons some health officials believed that a new AIDS superbug was in our midst was that the New York City man developed 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.

But since the Connecticut man first tested positive for HIV in 1993, the virus itself does not appear to be responsible for the rapid progression to full-blown AIDS, Blick says.

So why did the New York City man get sick so quickly?

Most likely, his behavior is the culprit, Blick says. The New York City man admitted not only to being promiscuous, but also to being a heavy user of crystal methamphetamine, an illicit drug that lowers inhibitions and increases risky sexual behavior.

Mark Wainberg, PhD, professor of medicine at McGill University in Montreal, says

multiple sex partners and repeated use of crystal "meth" may pack a wallop to the immune system, facilitating infection with multidrug-resistant HIV.

Another indication that a fast-acting new strain of HIV was not behind the man's rapid illness was a measurement of his CD4 cell count. Blick's study shows that his CD4 cell count (an indication of disease progression) responded to treatment, refuting the concept of a new aggressive strain.

Also, genetic susceptibility may have played a role in the man's condition, Blick says. Because this type of supervirulent virus was seen in only one case in February, some researchers had theorized that the man's individual genetic susceptibility, not the virus itself, was responsible for its rapid progression.

Wainberg tells WebMD that the study should end talk of a new AIDS superbug. "It's a well-done analysis that shows the strains are virtually identical," he says.

Get the Facts About HIV and AIDS

By Charlene Laino, reviewed by Brunilda Nazario, MD

SOURCES: 3rd IAS Conference on HIV Pathogenesis and Treatment, Rio de Janeiro, Brazil, July 24-27, 2005. Gary Blick, MD, medical and research director, Circle Medicine, Norwalk, Conn. Mark Wainberg, PhD, professor of medicine, McGill University, Montreal.