Some staff members at the U.S. Centers for Disease Control and Prevention may have suffered exposure to live anthrax bacteria following a lapse in safety protocols, officials said.

Scientists in a bioterrorism research lab mistakenly sent the live bacteria to fellow researchers in other labs at the center not equipped with the same security levels, believing what they were transferring were harmless samples of the pathogen, the agency said.

The CDC was monitoring as many as 75 workers in four separate laboratories and had provided them with antibiotics "out of an abundance of caution," but the "risk of infection is very low," agency officials said Thursday.

The bioterrorism lab apparently did not completely inactivate its samples before transferring them to other labs for further testing, labs that don't have the equipment necessary to safely handle live samples of the potentially deadly pathogen.

Believing the samples sent to them had been properly inactivated, workers in the lower-level laboratories were not wearing the proper protective clothing and equipment such as respirators when they handled them, the CDC said.

The problem was discovered after some of the original plates in the bioterrorism lab were collected for disposal and found to contain live colonies of B. anthracis.

Workers were immediately informed and the lower-level facilities were closed for environmental testing and decontamination, officials said.

There was no risk outside of those labs, they said.

"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," the centers said in a release.

An ongoing internal review would try to conclude why the safety protocols in place in the bioterrorism research facility were not followed, the release said.

"Given that CDC expert protocols were not followed, disciplinary action(s) will be taken as necessary," it said.

The disease anthrax is caused by bacteria that live in soil, and although it primarily affects grazing animals such as sheep, cattle and goats, humans can be infected by contact with affected animals or their hides or meat.

Although anthrax in humans can be cured, it needs to be diagnosed early, experts say, but people often don't realize they've been infected until the disease is past they point where it can be successfully treated.

In a bioterror attack that made headlines in 2001, someone sent anthrax bacteria using the U.S. mail, causing five deaths and making more than 20 people ill.