US Army mistakenly sent anthrax around the country and to South Korea

The US military mistakenly sent live anthrax bacteria to laboratories in nine states and a US air base in South Korea, after apparently failing to properly inactivate the bacteria last year, US officials said on Wednesday.

The Pentagon said there was no known suspected infection or risk to the public. But four US civilians have been started on preventive measures called post-exposure prophylaxis, which usually includes the anthrax vaccine, antibiotics or both.

Twenty-two personnel at the base in South Korea were also given precautionary medical measures although none had shown sign of exposure, the US military said. The four in the United States faced "minimal" risk, said Jason McDonald, a spokesman for the US Centres for Disease Control and Prevention (CDC), which has begun an investigation of the incident.

When anthrax becomes airborne, it can cause a deadly illness called inhalation anthrax. That occurred in 2001, when anthrax sent through the US mail to government and media targets killed five people.

The anthrax, which was initially sent from a Utah military lab, was meant to be shipped in an inactive state as part of efforts to develop a field-based test to identify biological threats, the Pentagon said.

"Out of an abundance of caution, [the Defence Department] has stopped the shipment of this material from its labs pending completion of the investigation," said Pentagon spokesman Colonel Steve Warren.

The CDC said it had launched an investigation of the mishap.