About 75 scientists working at federal government laboratories in Atlanta may have been exposed to live anthrax bacteria and are being offered treatment to prevent infection, the U.S. Centers for Disease Control and Prevention said in a statement Thursday.

The potential exposure took place after researchers failed to follow adequate protection procedures to inactivate anthrax samples at one CDC lab in Atlanta before transferring them to three other CDC labs not equipped to handle live anthrax bacteria, the statement said. Workers at those three labs, believing the samples were inactivated, were not wearing adequate personal protective equipment while handling the material.

Lab safety investigators also determined that between June 6 and June 13, procedures used in two of the three labs may have released spores into the air. When someone breathes in anthrax spores, they can develop inhalation anthrax, considered to be the most deadly form of anthrax.

The unintentional exposure was discovered June 13 when the original bacterial samples were gathered for disposal and found to contain live bacteria, the CDC said.

A CDC spokesman said he did not know of previous instances of unintentional exposure.

Out of an abundance of caution, the CDC is providing protective courses of antibiotics for the potentially exposed staff.

“Based on most of the potential exposure scenarios, the risk of infection is very low,” the statement said.

Other staff, family members and the public are not at risk of exposure.

Officials are investigating why proper procedures were not used. Decontamination is underway, and the labs will reopen when that is complete, a CDC spokesman said.

The CDC said disciplinary actions will be taken as necessary because protocols were not followed. Officials will also review safety protocols with all employees who work in this area, the statement said.

Anthrax is a serious infectious disease caused by bacteria known as Bacillus anthracis. The bacteria produce spores that are dormant and can live in the environment, such as soil, for decades. When spores get into an animal or a person, they can be activated and turned into “active growing cells,” according to the CDC.

After the Sept. 11, 2001, terrorist attacks on the World Trade Center and Pentagon, letters filled with a white powder containing anthrax spores were mailed to two U.S. senators’ offices and news media agencies along the East Coast. The powder form allowed the anthrax to float in the air and for it to be breathed in. The powder from these letters contaminated the postal facilities they were processed through, including the Brentwood mail-sorting facility in Northeast Washington, as well as the buildings where they were opened.

Of the 22 people who got sick with anthrax in 2001, five died. All of those who died had inhalation anthrax. In all, 43 people tested positive for exposure to anthrax, and 10,000 people were considered at risk of possible exposure to anthrax, the CDC said.