People with the condition complain of crawling, itching and stinging sensations and they often see tiny fibers or filaments that poke out of sores on their skin.

But the long-awaited government study, released on Wednesday in the journal PLoS One, found these fibers were mostly bits of cotton and nylon.

"We found no evidence that this condition is contagious, or that suggests the need for additional testing for an infectious disease as a potential cause," said Dr. Mark Eberhard, director of CDC's Division of Parasitic Diseases and Malaria, whose study appears in the journal PLoS One.

Eberhard said the study was not able to show the exact cause of the condition, but roughly half of the people in the study had illnesses, and most were psychiatric in nature.

Doctors have long suspected the condition was psychiatric rather than infectious.

Dr. Michael Cappello, a pediatric infectious disease expert at Yale University in New Haven Connecticut, has examined fibers taken from patients suffering from the condition.

"There really is not a controversy. The overwhelming number of physicians and investigators who have looked at this have come to the same conclusions," said Cappello, adding that it is commonly known by doctors as delusional parasitosis.

The strange condition was first described in 2002 by Mary Leitao of Pittsburgh who launched a website and advocacy campaign to identify a cause for the strange condition.

Prodded by an increasing number of reports and requests from lawmakers, the CDC embarked on a search for the cause in 2006.

"It was clear these folks were actually suffering from something, many of them suffering a great deal. We felt compelled to address it," Eberhard said in a telephone interview.

The CDC team used medical records from the managed care company Kaiser Permanente in Northern California, where many of the people with reported symptoms lived, and studied 115 people with the condition.

"We tested for a wide range of infectious diseases," Eberhard said.

Many of the patients had full clinical exams and skin biopsies. Patients filled out questionnaires about whether they had been exposed to solvents or household chemicals, and patients got a comprehensive neuropsychiatric evaluation.

They found no signs that the condition was caused by an infection or environmental exposure. And studies of the fibers taken from sores in the skin showed they were largely composed of cotton or nylon, consistent with fibers found in clothing and carpeting.

Eberhard said people likely were scratching their skin and fibers in the environment stuck to their sores.

And the condition is rare, affecting only 4 out of 100,000 patients enrolled in the health plan.

Eberhard said ruling out an infectious cause should give doctors much more information about how to treat patients.

"We're really thrilled," Eberhard said. "Our sense is this should ultimately be very good for people suffering from this condition."

Cappello, who was not involved with the research, said he is glad the paper has finally been published.

"It is my hope that the CDC's findings can be accepted and that this issue, at least for the time being, can be put to rest," he said.

The full study can be found here

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