Fifty one labs in 17 states and three foreign countries have been mailed samples of live anthrax, Pentagon officials have said on June 3.
The announcement doubled the number of incidents in the US. A smaller number of shipments were revealed last week.
Staff members at some of the labs have been treated for anthrax exposure as a precaution, but no-one has fallen ill.
The Pentagon has maintained there is no risk to the general public.
The Centers for Disease Control and Prevention (CDC) is leading the investigation into the incidents.
Photo Getty Images
According to defense official Robert Work, the number of affected laboratories is expected to rise.
Experts in biosafety have heavily criticized the lapse and called for improved precautions.
Symptoms of anthrax exposure include skin ulcers, nausea, vomiting and fever, and can cause death if untreated.
The military has ordered all of its labs that have previously received inactive anthrax samples to test them. In addition it is advising all labs to cease working with these samples until told otherwise.
Pentagon officials say there was no sign the live samples were sent due to any deliberate action.
The samples were mailed from a Utah army facility by commercial post to laboratories over the past 10 years.
In addition to the US labs, samples were sent to facilities in Australia, Canada and South Korea.
According to a CDC report, the US government infectious disease labs mishandled dangerous pathogens five times in the last decade.
In 2014, workers mishandled samples of anthrax and the highly-infectious H5N1 avian flu.
In response, the Center for Disease Control and Prevention (CDC) has closed the two labs involved.
The agency has also temporarily barred high-security labs from transporting dangerous pathogens.
There have been no reported infections from previous cases, and no-one potentially exposed to anthrax has shown signs of illness, CDC officials said.
“These events should never have happened,” CDC Director Tom Frieden told reporters on Friday.
A CDC report revealed that the US government infectious disease labs mishandled dangerous pathogens five times in the last decade
“I’m disappointed, and frankly I’m angry about it,” he said, adding later he was “astonished that this could have happened here”.
The incidents were listed in a report on a potential anthrax exposure in June, which occurred when researchers in a high-level biosecurity laboratory failed to follow proper procedures and did not deactivate the bacteria.
The samples were then moved to a lower-security lab in the agency’s Atlanta campus.
“This is not the first time an event of this nature has occurred at CDC, nor the first time it occurred from the [bioterror response] laboratory,” the report said.
The CDC only recently learned of a separate incident in May in which a sample of the avian flu was cross-contaminated with a highly pathogenic version of the virus and then shipped to an agriculture department laboratory.
The influenza lab and the bioterror response laboratory have been temporarily closed in response.
The other incidents reported by the CDC:
In 2006, the CDC’s bioterror lab transferred anthrax DNA to outside labs, believing the sample had been deactivated
Also in 2006, samples from a different CDC lab were found to contain live botulism bacteria
Researchers sent an infectious strain of the bacterium Brucella to outside laboratories as early as 2001 because they mistook it for a vaccine version; newly available test methods in 2009 confirmed it was not.
The revelations come just days after US officials announced long forgotten vials of smallpox left in a cardboard box had been discovered by a government scientist at a research centre near Washington.
The virus was located in six freeze-dried and sealed vials, according to the CDC.
On Friday, the CDC announced that at least two of the vials contained the live virus but that no infections had been reported as a result of the incident.
It is believed to be the first time unaccounted-for smallpox was been discovered in the US. The disease was officially declared eradicated in the 1980s.
The US Centers for Disease Control and Prevention (CDC) has said the number of health workers potentially exposed to anthrax has risen to 84.
The count of those at risk of illness has risen from the 75 initially reported on Thursday.
The CDC said researchers in a high-level biosecurity laboratory failed to follow proper procedures and did not inactivate the bacteria.
The exposure occurred in Atlanta at the weekend, the CDC has said.
The FBI is helping the CDC to investigate. The agency said it was too early to determine whether the transfer was accidental or intentional.
Eighty four Atlanta-based CDC scientists were possibly exposed to live anthrax
Symptoms of anthrax exposure include skin ulcers, nausea and vomiting and fever, and can lead to death.
Anthrax bacteria live primarily in inactive spores and are found naturally in the soil, but people can ingest or inhale spores, which can make the anthrax active.
Not everyone will fall sick when exposed to anthrax but left untreated, anthrax illness can turn very serious or lead to death.
Tests to confirm anthrax exposure include a blood swab.
Anthrax entered the US national consciousness in 2001, when shortly after the 9/11 attacks, letters containing powdered anthrax arrived at news organizations and the offices of US senators. Twenty-two people became ill and of those, five people died.
In a statement, the CDC said the anthrax samples were moved from a high-security lab to a lower-security one at their Atlanta headquarters.
“Workers, believing the samples were inactivated, were not wearing adequate personal protective equipment while handling the material,” the agency said.
“The unintentional exposure was discovered June 13 when the original bacterial plates were gathered for disposal and B. anthracis colonies [live bacteria] were found on the plates.”
The normal incubation period for anthrax illness can take up to seven days, but there have been cases of illness occurring as many as 60 days after exposure.
Fifty-four of the 84 identified employees had been treated at the CDC’s health clinic by Thursday morning, with two refusing a course of antibiotics. Twenty-seven employees also began the anthrax vaccine.