The sobering news came as two other people - an NBC worker in New York and a mail handler in New Jersey - were also suspected of having been exposed to anthrax.
And on Capitol Hill, anthrax was found in two more spots in the same southeast wing of the Hart Senate Office Building where an anthrax-laced letter was opened in the office of Senate Majority Leader Tom Daschle on Oct. 15. Spores found Wednesday in two sites in the Hart building will keep the southeast quadrant closed indefinitely, Daschle said.
Washington officials said that the stricken clerk, a 59-year-old man, was in guarded condition and that he did not come into contact with the only known letter contaminated with anthrax in the Washington area - the one sent to Daschle.
That raised the possibility that more than one tainted letter had been sent to the nation's capital - or that the Daschle letter had tainted another. "We cannot say that it was just one letter," FBI spokesman Chris Murray said.
Environmental testing will begin soon at all government mail rooms in the Washington area, officials said.
Homeland Security Director Tom Ridge said the anthrax sent to Daschle by "shadow soldiers" was the purest, most highly concentrated and potentially lethal of any analyzed.
"Clearly we are up against a shadow enemy, shadow soldiers, people who have no regard for human life. They are determined to murder innocent people," he said. "It is clear that the terrorists responsible for these attacks intended to use this anthrax as a weapon."
Earlier, Ridge had said the anthrax found in letters sent through the mail system had not been "weaponized."
The Daschle sample apparently contaminated the Brentwood post office in Washington, where two postal workers died and two others are hospitalized. That facility also processed mail for the State Department.
Postal officials have begun testing 200 postal offices along the East Coast and will spot-check others around the nation, Ridge said.
