Suggestions that a new, highly multidrug resistant and rapidly progressing strain of HIV has evolved in New York City and could become widespread have been refuted by the discovery of the probable patient source of the virus, according to a presentation here on Monday at the 3rd International AIDS Society (IAS) Conference on HIV Pathogenesis and Treatment.

The rapid progression to AIDS observed in a patient discovered earlier this year led the New York City Department of Health to issue a press release on February 11, 2005, warning of a possible new, highly virulent and multidrug resistant HIV strain. This was followed by reports in The Lancet and elsewhere.

The apparent source patient, “Patient Zero,” is a resident of Connecticut and his clinical course is typical of AIDS patients with his disease, behavior and medical compliance, said Dr. Gary Blick, medical and research director of Circle Medical LLC, Norwalk, Connecticut.

The patient’s viral replication capacity is 41 percent, and since he has become fully adherent to highly active antiretroviral treatment (HAART), his CD4 levels and viral copy number, measures of disease progression, have remained stable

“He is not a rapidly progressive patient,” Blick said. His life partner’s disease course is similarly unremarkable.

By contrast, the New York City patient, whose disease so alarmed clinicians, has shown a viral replication capacity as high as 136 percent, Blick said. The patient was infected with the virus about four months before he progressed to AIDS. That patient has a history of extensive unprotected sex and multiple partners, often while using crystal methamphetamine.

The Patient Zero identified in Connecticut carries a virus that is a 99.5 percent genetic match to that of the New York patient, Blick said. His life partner, who is also HIV positive, has a genetic match of 98.5 percent.

In addition to the genetic evidence of virus transmission, the patients involved were able to identify each other visually and confirmed anal-receptive or anal-insertive intercourse, Blick said.

Blick hypothesized that the rapid course and treatment resistance experienced by the New York patient can be attributed to unusual host factors, including an unusually active sexual lifestyle and heavy use of crystal methamphetamine.

It is also possible that this HIV strain is not as responsive to treatment or that these two factors are interacting to product this outcome, he said.

Blick added that the widespread practice of “poz-to-poz” unprotected sex, in which sexual partners who are both HIV positive fail to take precautions, may be riskier than previously assumed.