Pentagon officials yesterday insisted there was no threat to public health but the latest numbers showed small concentrations of suspected live anthrax were shipped to 51 labs in 17 states and the US capital Washington, as well as to Australia, Canada and a US base in South Korea.
When the Pentagon first acknowledged the problem last week, officials initially said more than a dozen labs were affected in nine states.
About 300 government and private laboratories work with anthrax in the United States, officials said.
Although officials played down fears of any serious health danger, the stream of embarrassing details in recent days has raised questions about the Pentagon's competence in managing the deadly pathogen.
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Lawmakers have blasted the Defence Department over the issue, accusing it of betraying the public's trust.
Yesterday's news conference at the Pentagon marked the first time senior officials had spoken publicly about the problem, which first came to light a week ago when a commercial lab in Maryland reported receiving a live anthrax sample.
Out of those four batches, which dated back to 2005, samples were sent out to labs across the country and abroad for research work -- including a facility next to the Pentagon.
The four live batches come from a total of 400 batches or "lots" of anthrax at four military facilities that handle the pathogens, including Dugway Proving Ground.
Officials have ordered that all anthrax held at the military repositories be tested to check for any further live bacteria, Work said.