A new, apparently more virulent form of a virus known as an adenovirus that usually causes nothing worse than a nasty cold is circulating around the United States, infecting at least 1,035 Americans in four states so far this year, hospitalizing dozens, and at least 10 have died.

Health officials say the virus does not seem to be causing life-threatening illness on a wide scale, and most people who develop colds or flu-like symptoms are at little or no risk. Likewise, most people infected by the suspect adenovirus do not appear to become seriously ill. But the germ appears to be spreading, and investigators are unsure how much of a threat it poses.

"This virus has the capability of causing severe respiratory illness in people of all ages, regardless of their medical condition," said John Su, a disease investigator for the Centers for Disease Control and Prevention based in Texas, where the largest outbreak is tapering off at an Air Force base after 10 months. Other outbreaks have been reported in Washington state and South Carolina, along with a single case in an infant in New York City.

There are 51 known strains of adenovirus, ubiquitous germs that cause many illnesses, including colds, pinkeye, bronchitis, stomach flu and a respiratory infection called boot camp flu that has long plagued soldiers. But adenovirus infections rarely have been life-threatening, especially for healthy young adults.

The new adenovirus is a variant of a strain known as adenovirus 14. First identified in Holland in 1955, it has caused sporadic outbreaks in Europe and Asia. No outbreaks, however, had ever been documented in the Western Hemisphere.

"What people need to understand is that there is a virus out there that can make you very, very sick," Su said. "If you have a bad cold and your symptoms keep getting worse, go see your doctor. This is nothing to be necessarily alarmed about. But it is important to be aware that this bug is out there."

(Agencies via Xinhua December 12, 2007)