Two House office buildings reopened Thursday for the first time in more than a week, but authorities say they are investigating the spread of anthrax in a Senate office building where the deadly bacteria was first detected.

And another government postal worker, this time working from a Sterling, Va. facility that serves the State Department, has tested positive for anthrax and is being treated at an area hospital. The Sterling operation, like all the other infected processing centers, receives its mail from the Washington-based Brentwood mail facility.

U.S. Capitol Police announced the discovery of anthrax in a Hart Senate office building freight elevator Wednesday night. Hart is the home of Senate Majority Leader Tom Daschle's office, where the first letterful of anthrax arrived on Oct. 15.  Another letter was subsequently sent to the office of House Speaker Dennis Hastert, R-Ill., in the Capitol, but was not opened.

"The swab sample was taken in the first floor freight elevator bank in the Hart Senate office building, which is in the southwest quadrant of the building. The investigators have told me this is a trace sample," meaning there was very little of the substance, said Capitol Police spokesman Lt. Dan Nichols on Thursday. 

Daschle's office is located on the fifth and sixth floors of the southeast quadrant, leading investigators to question how far the germs may have spread. The freight elevator was used by postal workers, according to Senate physician Dr. Jon Eisold.

Rayburn and Cannon on the House side opened to lawmakers, staff and the public at 9 a.m. Thursday. Longworth, the third building that houses representatives' offices, will not be open until at least Monday, Nichols said.

Health officials signed off on reopening the Russell Senate office buildings on Wednesday morning. Lawmakers who remain locked out of their offices will continue to work in makeshift offices in the General Accounting Office, Congress' investigative arm.

Nichols said investigators would try to determine how the anthrax reached the elevator area, saying they will try to track the possible path of Daschle's mail. The Hart building has been closed since the evening of Oct. 17.

It was the first time that authorities announced a new "hot spot" since last weekend when a mailroom in Ford House office building was said to be contaminated. That brings to five the number of spots where anthrax has been detected, including Daschle's office and two other mailrooms.

Nichols said they have cleaned with antibacterial foam contaminated mailrooms in the Dirksen Senate office building and the Ford House office building.

"After that foam was applied the rooms were remediated and then sealed. They remain sealed until further notice," Nichols said.

Ford will reopen on Friday with its mailroom sealed off, Nichols said.

Thursday, Daschle, D-S.D., said he hoped the Dirksen Senate building would be useable as early as Friday, and that Hart could be opened after authorities seal off the contaminated areas over the weekend.

"I am very confident that we will be able to seal it in a way that will provide us complete confidence that we can access the rest of the building without any hazardous exposure, and I think it is importnat that we get underway and get that job done," he said. 

As part of that plan, the Senate physician authorized senators or their designated aides to enter closed Senate buildings Thursday to retrieve personal or work-related items.  They will not be allowed to enter sealed off areas where anthrax was located.

So far, 28 Senate aides and Capitol police have tested positive for anthrax exposure.

Eisold said those positives are "truly positive," meaning they have been verified in confirmatory tests. No new positives have been found on other congressional employees.

But one more individual who is being treated for possible anthrax at Holy Cross Hospital in Silver Spring, Md., may have been exposed to the bacteria while in the Capitol complex.

That patient is a woman who works for an electronic news organization and was outside Daschle's office the day the letter arrived, said Mike Hall, a hospital spokesman.

Hall said she had flu-like symptoms and is in stable condition. A diagnosis is expected Thursday, he said.

Eisold said that he can't be too cautious with workers on Capitol Hill right now but he "would urge people not to jump ahead of the clinical situation." 

"I have good reason to believe that this person will turn out to be fine," he said..

Other than that, Eisold said he is concerned about anybody who was on the Hill and in the Hart building.

 The Associated Press contributed to this report.