WASHINGTON (AP) - An apparent mix-up at a military laboratory is being blamed for the anthrax scare that closed three area mail facilities that handle Pentagon-bound mail, and prompted nearly 900 workers to receive antibiotics.
The two-day scare that recalled the fatal bioterrorism attacks of 2001 turned out to be a false alarm after definitive tests at two facilities came back negative Tuesday for the deadly spores.
Officials believe the confusion stemmed from a mistake at a Defense Department laboratory at Fort Detrick, Md. Officials there apparently mixed up a sample of actual anthrax that is kept on hand for comparison purposes with the sample taken from a Pentagon mailroom, a senior administration official said.
Later tests proved negative and officials realized their error, the official said, speaking on condition of anonymity.
Warning signs at the two Pentagon mail facilities on Monday led to the comprehensive testing. Nearly 900 workers were given precautionary antibiotics, and officials closed three mail facilities at the Pentagon and in Washington.
"We have nothing to suggest anything remotely like the events of October 2001, and we hope that with further information we'll be able to completely rule out any threat at all," Dr. William Winkenwerder, assistant defense secretary for health affairs, said.
Winkenwerder said some additional tests remained incomplete. All tests that have been completed on samples from both Pentagon facilities have come back negative, he said.
Workers who were advised to take antibiotics would be told to stop if those tests also proved negative, Winkenwerder said.
In the meantime, area hospitals were advised to look out for respiratory problems, rashes and flu-like symptoms that could signal exposure to anthrax.
In 2001 anthrax-by-mail attacks killed five people and panicked Americans still raw from the attacks of Sept. 11, 2001. Since then, scores of initial tests in government mailrooms have falsely reported anthrax. But this week's alarm was set off by two alert systems that independently suggested the presence of the bacteria - what officials now believe was a coincidence.
First, a filter on a device that screens mail for chemical and biological agents on the Pentagon grounds tested positive for anthrax. Separately, an alert was set off at a nearby satellite mail processing facility. Officials set out to retest the initial filter and gathered additional samples from the facilities for testing.
Initially, tests suggested anthrax might be present, according to a counterterrorism official close to the investigation. Subsequent testing of both the initial filter and of other samples at both locations came back negative, Winkenwerder said.
"We're very encouraged with the information that we now have in hand," he said.
As a precaution, antibiotics were given to 166 employees at a post office processing center in the District of Columbia and to about 700 workers at the facility on the Pentagon grounds in Arlington, Va., and the satellite facility several miles away in Fairfax County, Va.
Virginia officials said they received fewer than 10 calls from concerned residents, perhaps indicating a change in how the public confronts a potential crisis. State homeland security director George W. Foresman said the government response to the scare - on the local, state and federal levels - was far better coordinated than in 2001.
"The unfortunate reality of when we have an event like this is we become better honed in our skill set in dealing with it," Foresman said.
Anthrax can be spread through contact with the skin. A more serious form of the disease, inhalation anthrax, is contracted by breathing in spores. After the 2001 attacks, health officials concluded that some people can contract the disease through exposure to a small number of the microbes.
Associated Press Writer Lara Jakes Jordan contributed to this report.