WASHINGTON (REUTERS) - As many as 75 scientists working in US federal government laboratories in Atlanta may have been exposed to live anthrax bacteria and are being offered treatment to prevent infection from the deadly organism, the US Centers for Disease Control and Prevention said on Thursday.
The potential exposure occurred after researchers working in a high-level biosecurity laboratory at the agency's Atlanta campus failed to follow proper procedures to inactivate the bacteria.
They then transferred the samples, which may have contained live bacteria, to lower-security CDC labs not equipped to handle live anthrax.
Two of the three labs conducted research that may have aerosolized the spores, the CDC said.
Environmental sampling was done and the lab areas are closed until decontamination is complete.
Dr Paul Meechan, director of the environmental health and safety compliance office at the CDC, said the agency discovered the potential exposure on June 13 and immediately began contacting individuals working in the labs who may have unknowingly handled live anthrax bacteria.
"No employee has shown any symptoms of anthrax illness," Meechan said.
Meechan said the CDC is conducting an internal investigation to discover how the exposure occurred and said disciplinary measures would be taken if warranted.
"This should not have happened," he said.
For those exposed, he said, "We're taking care of it. We will not let our people be at risk."
The normal incubation period for anthrax can take up to five to seven days, though there are documented cases of the illness occurring some 60 days after exposure, Meechan said.
As many as seven researchers may have come into direct contact with the live anthrax, he said.
But the agency is casting as wide a net as possible to make sure all employees at the agency who may have walked into any of the labs at risk are being offered treatment.
Around 75 people are being offered a 60-day course of treatment with the antibiotic ciprofloxacin as well as an injection with an anthrax vaccine.
Meechan said it is too early to determine whether the transfer was accidental or intentional.
He said that all employees who were doing procedures to inactivate the bacteria were working in a biosecurity laboratory and had passed a security check.
The CDC said in a statement it has reported the lab-safety incident to the Federal Select Agent Program, which oversees the use and transfer of biological agents and toxins that pose a severe threat to the public.
CDC spokesman Tom Skinner did not say whether the Federal Bureau of Investigation was investigating.
The FBI was not immediately available to comment.
Henry Waxman, the top Democrat on the House Energy and Commerce Committee, said he is "extremely concerned" but said "we understand CDC has taken swift action to respond to the possible exposure and will be investigating how this exposure occurred and appropriate measures to prevent such an event from happening in the future."
Dr William Schaffner, an infectious diseases expert at Vanderbilt University Medical Center, said the potential exposures are still "profoundly unfortunate and serious."
"What's good about it is the exposures are minimal," he said.
CDC responded appropriately, aggressively and transparently. The risk to the individual is low and to the surrounding community, essentially nil."
Schaffner said it is not yet clear exactly what the breach in infection control protocol was, but said, "Whatever it was, it should not have happened."
Anthrax is a potentially deadly infectious disease caused by exposure to the bacterium Bacillus anthracis.
The bacteria most commonly affect hoofed animals such as goats, but people can also become infected. Infection can occur through a cut in the skin, breathing in anthrax spores or eating tainted meat.
Meechan said CDC workers in the lower-security labs were likely not wearing masks.
With anthrax, the biggest threat is inhalation anthrax, in which bacterial spores enter the lungs where they germinate before actually causing disease, a process that can take one to six days.
Once they germinate, they release toxins that can cause internal bleeding, swelling and tissue death.
Inhalation anthrax occurs in two stages.
In the first stage, symptoms resemble a cold or the flu.
In the second stage, anthrax causes fever, severe shortness of breath and shock.
About 90 per cent of people with second-stage inhalation anthrax die, even after antibiotic treatment.