13:12 16 March 2005
NewScientist.com news service
Kelly Young and Damian Carrington
An anthrax scare involving three postal centres serving the US Pentagon has been blamed on a mix-up of samples. The scare has led to about 900 people receiving antibiotics and caused the stock market to dip.
A senior military official told reporters late on Tuesday of "quality control problems" at a laboratory contracted by the US Department of Defense. Speaking anonymously, he said it appeared likely that a sample of anthrax used for calibration had somehow contaminated an air filter from the Pentagon Remote Delivery Facility, sent for routine testing on 10 March.
Following the positive test result, a further 70 surface swabs and air samples were taken from the facility but none have shown any presence of the bacteria, the Pentagon says. The follow-up tests were being conducted at Fort Detrick, Maryland, and, as a precaution, hundreds of employees were put on a three-day dose of antibiotics.
William Winkenwerder, assistant secretary of defence for health affairs, said that not all the test results had yet come back, but "we hope that with further information we'll be able to completely rule out any threat at all'.
Initial speculation suggested that a PCR-based test (polymerase chain reaction) to detect specific segments of the anthrax genome had caused the alert. "That test is prone to false positives," said Sandro Cinti, at the University of Michigan.
Even if anthrax really had been detected, the health threat is likely to have been small, because mail at the Pentagon facilities is irradiated to kill any microbes. However, there could have been a threat to postal workers who handled any contaminated mail before it arrived at the Pentagon, when any anthrax bacilli would still have been alive.
The US Postal Service facility that feeds the Pentagon its mail, at V Street in Washington, DC, was closed after the initial alarm. "We had no evidence that anything was amiss at V Street," Jerry McKiernan, postal spokesman, told New Scientist, but as a precaution, all 209 employees were given doses of the antibiotic, Cipro.
Another mail facility in Fairfax County, Virginia, closed down on Monday after a sorting machine shut down automatically. Fearing the machine had detected anthrax, the Fairfax County Health Department told people to wash their hands, faces, jewellery and spectacles. When they got home, they were asked to carefully remove their clothes and bag them, before taking a shower.
The Bacillus anthracis bacterium causes the disease anthrax, but cannot be transmitted from person to person. In 2001, 22 people were infected with anthrax sent through US mail and 5 died. The person who sent the anthrax remains at large.