A letter postmarked in Trenton, N.J. -- containing anthrax -- was delivered to Daschle's office in the Senate Hart Office Building Monday.
By Wednesday evening, according to Daschle and public health officials from Health and Human Services, and the Centers for Disease Control and Prevention, told reporters that "several thousand" staffers, journalists and Capitol visitors had been tested with nasal swabs. Of the 155 people in the immediate vicinity of the envelope, who were all tested Monday, 31 had anthrax exposure.
According to Assistant Surgeon General Dr. Ken Moritsugi, 23 staffers in Daschle's office, three in Wisconsin Democrat Russ Feingold's office and five Capitol Hill Police officers had shown signs of exposure, but not infection.
Feingold has an office next to Daschle's and the two reportedly have mailrooms that virtually touch, according to Daschle staff.
Only those individuals who worked in the immediate vicinity of the exposure or responded to the crime scene have shown signs of exposure, Moritsugi said.
Daschle repeatedly stressed that this did not mean they had contracted anthrax and he was "confident" that their immediate treatment with antibiotics would prevent the disease.
"I'm concerned for my staff. I'm angered that this has happened. But I feel confident about those steps and about the fact that everyone will be okay," Daschle said.
Although the Senate will remain in session through Thursday, all three Senate office buildings will be closed and most committees, reportedly, are planning to cancel hearings, although some could be held in the Library of Congress buildings nearby.
Dennis Hastert, R-Il., and Richard Gephardt, D-Mo., the Republican and Democratic House leaders, announced about 10:20 a.m. that the House of Representatives would recess at the close of business Wednesday to allow a scan of the House office buildings for the presence of anthrax.
"We want to make sure the buildings are environmentally safe," Hastert said at an impromptu briefing for reporters.
He said the decision to shut down the House, send the employees home and close buildings to visitors, was triggered by "the discovery that this stuff had gotten into the ventilation system..."
Hastert later admitted that this was "only a possibility," and Daschle later said that no anthrax had been found anywhere other than his own office and the Senate mailroom in the Dirksen Office building.
A little over two hours later, Sens. Daschle and Trent Lott, the Senate Democratic and Republican leaders, held a news conference in which they said the Senate had decided not to halt its work.
Daschle said there was no evidence that the anthrax had gotten into the Capitol Building and no scientific reason to support calling the Senate into recess. They presented several government officials to report on the anthrax investigation at the Capitol.
Robert Gibbs, the program manager of the Defense Advanced Research Projects Agency, which is doing the environmental scan, confirmed that anthrax had been found in a mailroom that had handled the Daschle letter, but he said "we have no positive tests, no positive indication of contamination spread within the vent system."
Daschle's office later said the mailroom that processed the letter was located in the Dirksen Senate Office Building, an older structure than Hart, two long city blocks from the Capitol. Those two office buildings have thousands of employees in them and are connected by ventilation and underground passages.
At the time the letter arrived Monday, there were hundreds of people visiting Capitol Hill on different business, and the medical authorities are trying to locate and test visitors to Hart and Dirksen. Workers in the Supreme Court who went to a federal credit union in Hart are also being tested.
Facing criticism from Senate Republicans and some House members on his decision to close the House, Speaker Hastert about 1:30 p.m. clarified his earlier statements about his decision to close the entire House of Representatives complex -- half the Capitol and several office buildings. He explained that the decision stemmed from a combination of a suspicious package and the type of anthrax found in Daschle's office.
The package was reportedly sent to one of Hastert's offices, this one on the third floor of the Capitol building itself.
"The package met the profile and the Capitol Police came and took it away," he said. Results from field tests on the package were not immediately available.
Hastert said the decision to close the House side of the Capitol campus came after discussions with Daschle and Homeland Security director Tom Ridge. This runs counter to earlier reports and statements by Senate staff that Hastert did not consult with the Senate Majority leader before he decided to close the House.
"We'll finish our work today, adjourn the House tonight and allow members to go home, so we can go ahead and do our work on Tuesday," he said. "We've asked the appropriate bodies to come in and do a sweep of the House of Representatives and the campus of the House of Representatives to make sure. We don't know if there's a package that's arrived here, or a mailing machine or a package that has been opened."
Hastert said that the decision to close the campus was an easy one because, "we wanted to make sure that we did not have any spores around."
But the decision ran headlong into the U.S. Senate, which faced the same situation with the opposite decision: to stay in business as usual mode.
When asked by reporters why the House -- which has not seen exposure to anthrax yet -- would leave, while the Senate -- which has 31 employees exposed -- would stay at work for the remainder of the week, Hastert refused to answer.
"You're going to have to ask the senators," he said.
Sen. Bill Frist, R-Tenn., a cardiovascular surgeon, explained some of the miscommunications stem from the nature of a fluid -- and never before seen -- medical emergency in the halls of Congress.
"We don't have all of the answers today," he said. "It's an evolving situation and has been a seminal event."
But Frist, Daschle and numerous public health officials have stressed that each exposed person is unlikely to develop anthrax and that the situation appears to have stabilized as investigators work to uncover additional details of the exposure.