A US military base in Utah sent live anthrax samples to 51 labs in 17 US states, Washington, DC and three foreign nations, more than previously disclosed, and the number may rise, the Pentagon said on Wednesday.
Investigators were trying to ascertain whether the inadvertent shipments of the pathogen, which can be used as a biological weapon, stemmed from quality control problems at the base, the Dugway Proving Ground, Pentagon officials said.
No one at the labs has been infected and there is no known risk to the public, officials said.
A number of US military facilities for the past decade have shipped what were supposed to be inactivated, or killed, anthrax samples to outside labs to develop counter-measures to biological weapons. The one in Utah is the only one known to have sent samples that proved to have live bacterial spores.
The officials told a briefing they expect to learn that the number of labs receiving such shipments is even higher and that more shipments than currently known contained live anthrax rather than the inactivated version.
"As of this point, there is absolutely nothing to indicate that this would be somebody who is trying to do this deliberately," Deputy Defense Secretary Bob Work said.
The spore concentrations in the liquid samples were too low to infect a healthy person, Work said.
The Pentagon last week ordered a 30-day review of procedures on killing the live anthrax through gamma-ray irradiation.
Pentagon acquisition chief Frank Kendall said officials were testing more than 400 anthrax batches to determine how many were not successfully killed. He said at least four batches had been found with live spores, and testing continued.
The 51 commercial, academic and federal labs had received the live samples since 2006.
The Pentagon said the labs were in California, Delaware, Maryland, Massachusetts, New Jersey, New York, Tennessee, Texas, Utah, Virginia, Washington, Wisconsin, Arizona, Florida, Illinois, Ohio, North Carolina, Washington, DC, Australia, South Korea and Canada.
Officials said 31 people, including 23 Defense Department employees and eight US civilians, were taking preventive measures to guard against infection. These usually included the anthrax vaccine, antibiotics or both.
Commander Franca Jones, Pentagon director of medical programmes for chemical and biological defence, said officials could not yet say how many total samples were shipped by the Pentagon from the 400 batches being tested.