The US Centres for Disease Control (CDC) said suspect samples from Dugway had been sent to 18 labs in nine US states and a military base in South Korea.
Later the Pentagon said the army may have sent live anthrax to a laboratory in Australia in 2008.
CDC spokeswoman Kristen Nordlund said the agency was testing to see which samples were live. Findings were expected next week.
Wisconsin commercial laboratory, BBI Detection of Madison, which employs fewer than 20 people, confirmed it received live spores last week. No employees got sick or were in danger, and there was no danger to the public, said Jackie Lustig, a spokeswoman for Massachusetts-based Alere Inc, which owns BBI. However, the lab remains partially closed.
Four lab workers in Texas, Delaware and Wisconsin have been put on antibiotics as a precaution, the CDC said.
As well, 22 military and civilian personnel were placed under preventive treatment at Osan air base in South Korea, the Pentagon said.
The anthrax samples were supposed to have been rendered inactive by irradiation at a US Army facility in Utah.
Military and health officials launched a probe after a commercial lab in Maryland last week found a live sample of anthrax in a shipment from Dugway.
It was not clear precisely when samples were sent or where the samples were sent, other than Australia, officials said.
"We are still trying to figure out where the samples were sent," said a US official.
US military and health authorities insisted no threat was posed to public health and there were no suspected cases of infection.
The anthrax bacteria sent out was part of a Pentagon effort "to develop a new diagnostic test to identify biological threats", the CDC said.
US government laboratories came under fire last year over reports of sloppy management of deadly bacteria.
As a result, 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.
The lethal anthrax disease is spread by spores and has been used for bioweapons programmes in the US and elsewhere.
In 2001 powdered anthrax spores were found in letters mailed in the United States. Out of 22 people who were infected, five died.
Anthrax spores are deadly unless a patient is promptly treated with large doses of antibiotics.
South Australian independent senator Nick Xenophon has called for an explanation of how live anthrax was sent to Australia.
"If the Government can put in a big effort in terms of Johnny Depp's dogs, then I reckon they should give a full explanation for something as serious as this," Xenophon said.
"If this incident was covered up in any way, what else has been covered up?"
-AAP
