A military base in Utah shipped anthrax samples to 66 laboratories in 19 states.
The updated numbers came as authorities stepped up precautionary treatment measures, Reuters reported Tuesday.
Thirty-one people are receiving such treatment for exposure to live anthrax, the report said, citing army colonel Steve Warren, a Defense Department spokesman.
The figure is unchanged since the Pentagon’s last update on the incident.
Warren said one new state, Pennsylvania, had been added to the list of locations where live anthrax had been sent.
In addition to the US states and Washington, the pathogen was sent to South Korea, Canada and Australia.
Investigators are trying to ascertain whether the accidental shipments of the anthrax, 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 countermeasures to biological weapons.
The one in Utah is the only one known to have sent samples that proved to have live bacterial spores.
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