The CDC announced Friday that at least 84 government scientists could have been exposed to anthrax while handling live samples of the disease at three laboratories in Georgia, nine more than the agency reported on Thursday.
The Centers for Disease Control and Prevention originally announced that 75 workers may have been exposed to anthrax, a lethal and infectious disease, while conducting experiments at its Atlanta facility in early June. But officials expect that number will continue to rise as news of the breach spreads.
"Right now we have an excess of 80 individuals," Illeana Arias, CDC deputy director, told NBC News. "We expect that number may even grow...because we're trying to make that available to as many people as possible in order to make sure there are no adverse consequences to health of any of our employees as a result of what happened."
The breach occurred when the Atlanta center's Bioterror Rapid Response and Advanced Technology lab failed to kill samples of the bacterium Bacillus anthracis, which causes anthrax. At the time the lab was in the process of trying out a new method for sterilizing the bacteria, which involved using chemicals instead of radiation, Reuters reported.
Somehow the samples, while still alive, were sent to two other labs and used in experiments between June 6 and June 13. It wasn't until the samples were to be thrown out when the mistake was detected.
Doses of the powerful antibiotic ciprofloxacin were given to 34 employees as of Friday, Reuters reported. Another 20 were taking the antibiotic doxycycline and at least 27 were given an anthrax vaccine to prevent infection, the agency said.
The rest of the workers refused the offered medication, CDC spokesman Tom Skinner told NBC News.
So far no cases of anthrax have been reported. Officials are monitoring the workers for sings of symptoms, which include internal bleeding and swelling as the bacteria kills tissue. Tests for the disease include taking blood samples.
It can take up to two months for signs of the disease to show, according to the CDC.
The agency said the public is not at risk of infection. The investigation into the breach is ongoing.
Anthrax can infect the body through inhalation or open wounds in the skin. If inhaled, the disease is nearly 90 percent fatal, even with antibiotics.
