As many as 22 people in South Korea and four US lab workers may have been exposed to anthrax after the American military accidentally shipped out at least one live sample, officials said.
The four lab employees were undergoing medical treatment as a precaution after the military sent the sample inside the country to a commercial lab in Maryland.
As many as 22 personnel may have been exposed to anthrax during a laboratory training exercise at the US Osan Air Force Base in South Korea using samples shipped from the same batch, a military statement confirmed. The sample was being used in a self-contained "laboratory environment" on the base.
"Hazardous material teams immediately cordoned off the facility, decontaminated it... and destroyed the agent," the statement said.
In addition to the military base in South Korea, more than a dozen other government and commercial labs in nine US states had received samples from the accidental shipment, officials said.
All of the samples had been irradiated in March last year at a military lab in Utah and were supposed to be "dead."
But on Friday, a private firm in Maryland notified authorities that its sample was still active, setting off an urgent review of all material sent out to other labs.
Four people at three different companies that had "worked with the live anthrax" were receiving post-exposure treatment as a precaution.
The Pentagon and health officials said the incident posed no threat to public health.
"There is no known risk to the general public, and there are no suspected or confirmed cases of anthrax infection in potentially exposed lab workers," Pentagon spokesman Colonel Steven Warren said in a statement.
The Centers for Disease Control and Prevention (CDC), backed up by the Defense Department, is investigating the mishap.
The CDC said in a statement the investigation is examining if other labs had received live samples and conducting a safety review. However it is still unclear what had gone wrong and how many labs might be affected.
The Defense Department lab in Utah, Dugway Proving Grounds, routinely transfers "dead" anthrax samples for scientific research.
The lab was working on a project to detect biological threats in the field, Warren said.
The other labs in the United states receiving samples from the original batch were located in California, Delaware, Maryland, New Jersey, New York, Tennessee, Texas, Wisconsin and Virginia.
The lethal anthrax disease is spread by spores and previously was used for bioweapons programs in the United States and elsewhere. Washington scrapped its bioweapons effort as part of an international treaty in 1975.
Friday's announcement comes less than a year since health officials faced severe criticism over a spate of safety lapses at CDC labs handling deadly pathogens, including anthrax.
As a result of those lapses, health officials suspended the shipment of potentially dangerous pathogens from government labs in Atlanta and the CDC shut down two of its laboratories, including one implicated in the mishandling of anthrax samples.
Investigators from the Agriculture Department last year found anthrax was stored in unlocked refrigerators in an unrestricted corridor, and that dangerous materials were transferred using resealable plastic bags.