Updated

Health officials ordered anthrax testing at thousands more mail rooms across the Washington area but continued to insist that postal customers had very little risk of falling victim to the spreading bioterror. Fresh evidence of the bacteria turned up on Capitol Hill and at a growing list of government mail rooms.

Concern over the mail delivery system mounted with anthrax now spotted at more than 10 postal facilities in the area, and health officials hoped to stop its spread with an escalation of testing and treatment.

"We're getting in front of the fire," said Dr. Patrick Meehan of the Centers for Disease Control and Prevention. But he warned that thousands more people who work with the mail will need to begin taking preventive antibiotics. "It could be an astronomical number," he said.

Three weeks into the anthrax-by-letter scare, officials said they would begin testing at between 2,000 and 4,000 sites that receive mail from the city's Brentwood postal processing facility — large apartment buildings possibly among them — and recommend antibiotics for all who work at them.

Trace amounts of anthrax were detected in the offices of three House members in the Longworth Office Building, shuttered for more than a week. Mail delivery on Capitol Hill has been suspended even longer.

The majestic Supreme Court building also fell victim to a spreading bioterrorism scare, as officials ordered it shuttered for testing after a trace amount of anthrax was detected in an offsite mail center. Anthrax was also reported at a CIA mail facility, at Walter Reed Army Medical Center and a Washington post office — all of which receive mail from the Brentwood facility.

Officials emphasized that people who work full-time with mail are at a higher risk than postal customers, who only touch the letters meant for them. For typical Americans, Meehan said, the mail poses "an incredibly remote risk." Still, they recommended that people look at their mail closely and wash their hands after touching anything suspicious.