The United States Department of Agriculture (USDA) is taking over investigation into a breach of security, which exposed at least 84 government workers to anthrax. 

On 19 June, the CDC announced 75 people had been exposed to the potentially-hazardous bacteria Bacillus anthracis. The official number of workers exposed was raised by nine people soon after. 

Centers for Disease Control and Prevention (CDC) workers were exposed to the potentially deadly virus. These incidents occurred at three CDC locations. Investigations of this type are normally handled by the agency's Division of Select Agents and Toxins (DSAT), a group with experience involving similar pathogens. 

In order to avoid a conflict of interest, investigation of the CDC safety breach will be managed by the Animal and Plant Health Inspection Service (APHIS), operated by the USDA. 

At least 32 workers are being treated with a powerful antibiotic, Cipro, also called ciprofloxacin. At least 20 people were prescribed doxycycline, a different antibiotic. The CDC reported as many as 27 people are being treated with an anthrax vaccine to prevent infection. 

No illnesses or symptoms have yet been reported among anyone exposed to the deadly pathogen. 

"Based on the review to date, CDC believes that other CDC staff, family members, and the general public are not at risk of exposure and do not need to take any protective action," agency officials stated. 

The accident occurred at in the Bioterror Rapid Response and Advanced Technology laboratory. Scientists there sent live anthrax from their high-security facility to a low-security station without successfully neutralizing the bacteria. 

Samples of the pathogen were placed in a petri dish, containing nutrients. After 24 hours, there was no new growth of bacteria, and the culture was assumed to be dead. Researchers accidentally left the dishes warming in an incubator for a week, and when they came out, additional anthrax was growing on the plate. This was proof the samples sent to the second facility were alive. Researchers there are developing chemical techniques to kill bacteria, replacing current techniques, which use radiation. 

Anthrax released in the incident is the same highly-dangerous Ames strain used in terror attacks in the wake of 9-11.

Researchers at the CDC were investigating new methods of quickly identifying anthrax in samples of unknown materials, a procedure that could minimize the effect of any similar attack in the future. 

The agency has been criticized for several safety breeches, as far back as 2007. 

Congress has started its own investigation of safety procedures at CDC facilities. White House officials say the President was briefed on the situation by counter-terrorism adviser Lisa Monaco on the 20 June. 

The Select Agent Program controls the use, transfer and possession of biological toxins and other agents that could pose health hazards to people and wildlife.