Researchers have identified a mysterious new disease that has left scores of people in Asia and some in the United States with AIDS-like symptoms even though they are not infected with HIV.

The patients' immune systems become damaged, leaving them unable to fend off germs as healthy people do. What triggers this isn't known, but the disease does not seem to be contagious.

This is another kind of acquired immune deficiency that is not inherited and occurs in adults, but doesn't spread the way AIDS does through a virus, said Dr. Sarah Browne, a scientist at the National Institute of Allergy and Infectious Diseases.

She helped lead the study with researchers in Thailand and Taiwan where most of the cases have been found since 2004. Their report is in Thursday's New England Journal of Medicine.

The disease develops around age 50 on average but does not run in families, which makes it unlikely that a single gene is responsible, Browne said. Some patients have died of overwhelming infections, including some Asians now living in the US, although Browne could not estimate how many.

Kim Nguyen, 62, a seamstress from Vietnam who has lived in Tennessee since 1975, was gravely ill when she sought help for a persistent fever, infections throughout her bones and other bizarre symptoms in 2009. She had been sick off and on for several years and had visited Vietnam in 1995 and again in early 2009.

 Nguyen (pronounced "when") was referred to specialists at the National Institutes of Health who had been tracking similar cases. She spent nearly a year at an NIH hospital in Bethesda, and is there now for monitoring and further treatment.

"I feel great now," she said today. But when she was sick, "I felt dizzy, headaches, almost fell down," she said. "I could not eat anything."

AIDS is a specific disease, and it stands for acquired immune deficiency syndrome. That means the immune system becomes impaired during someone's lifetime, rather than from inherited gene defects like the "bubble babies" who are born unable to fight off germs.

The fact that nearly all the patients so far have been Asian or Asian-born people living elsewhere suggests that genetic factors and something in the environment such as an infection may trigger the disease, researchers conclude.

The first cases turned up in 2004 and Browne's study enrolled about 100 people in six months.