A new strain of a virus that causes the common cold may be responsible for the emergence of a mysterious respiratory disease that has killed 17 people and sickened hundreds around the world, U.S. health experts said Monday.

The U.S. Centers for Disease Control and Prevention said tissue samples taken from two patients infected in a recent global outbreak of severe acute respiratory syndrome (SARS) had tested positive for a new form of coronavirus.

The same strain of the virus has also been found in lung secretions and other genetic material taken from seven other patients, the CDC said.

Coronaviruses, so-named because they have a crown-like appearance when seen under a microscope, are the second leading cause of colds in humans and are often responsible for upper respiratory infections in premature infants.

“We’re culturing it and finding it in actual tissue samples,” Dr. Julie Gerberding, director of the CDC, told reporters during a news conference in Atlanta. “In scientific terms, this is very strong evidence.”

But she said a lot more research needed to be done.

More than 400 people have contracted an illness that resembles pneumonia in the past two months, according to the World Health Organization, which sent out a global health alert about the outbreak two weeks ago.

The WHO figure excludes 39 suspected cases in the United States.

The outbreak, which may be linked to a wave of similar illnesses that began in southern China in November 2002, has spread through Hong Kong, Vietnam and other parts of Asia.

A handful of cases, including three deaths, have been reported in Canada.

The illness begins with a high fever and dry cough that can lead to breathing difficulties and force the use of a respirator. The CDC said most of the U.S. cases were among people who had recently traveled to Asia.

Other cases have occurred among health care workers or relatives with close contact to those who have taken ill.

“We are not seeing it spread in the community at this moment,” said Gerberding, who added that healthy people could expect to survive if they contracted the disease.