The Postal Service closed 11 Washington, D.C.-area post offices Thursday while authorities ran tests to determine whether anthrax was detected at the Navy site that handles mail for federal agencies.
Postal Service spokesman Azeezaly Jaffer said authorities decided "out of an abundance of caution" to close the facilities and test them for any biohazard contamination.
There was no indication any of 1,200 to 1,500 postal workers involved were exposed to anthrax, and Jaffer said no employees had been offered antibiotics.
Equipment that routinely monitors the air at the Naval Automated Processing Facility in the District of Columbia indicated Wednesday the presence of "small amounts of biological pathogens, possibly anthrax," said Rachael Sunbarger, a Homeland Security spokeswoman.
After the initial field test, eight air samples were sent to Fort Detrick, Md., for testing, according to Lt. Cmdr. Edward Zeigler, spokesman for the Naval District of Washington. One sample tested positive for anthrax and seven tested negative, he said.
As a result, more testing was being done, he said.
A Navy spokesman at the Pentagon, Cmdr. Conrad Chun, said the Fort Detrick test showed a spore count of 138. Someone would have to breathe 8,000 to 10,000 spores to become infected by anthrax, according to the federal Centers for Disease Control and Prevention.
Most of the mail moving through the Navy mail station was processed by the Postal Service's V Street facility, which handles government mail, and it was closed, Jaffer said.
Later, however, it was determined that a contractor that transported the mail to the Navy site had also collected mail from 10 other facilities in the District of Columbia, Maryland and Virginia. All were closed.
The contractor, Shaw Inc., participated in the testing.
Only a few people work at the automated naval site. Chun said the workers were wearing protective clothing and an air monitor worked as designed. Mail is screened there before going to a mail handling facility nearby, he said. The facility, which also handles mail distributed to Navy personnel throughout the Washington area, also was closed.
Chun said the matter was being further investigated by the FBI, the Naval Criminal Investigative Service, postal inspectors and others.
All mail destined for Congress and federal agencies is irradiated before being delivered to the postal facilities.