FILE - A scientist examines a package for anthrax spores.
FILE - A scientist examines a package for anthrax spores.

CHICAGO - Scientists at the U.S. Centers for Disease Control and Prevention are conducting tests to see whether the procedure they followed to kill anthrax, although flawed by their own standards, may nevertheless have killed the potentially deadly pathogen before it was sent to less-secure laboratories, where employees work without adequate protective gear.

If they are right, it may mean dozens of scientists and staff, who were given a vaccine and powerful antibiotics to prevent anthrax infection, may never actually have been in danger of anthrax disease, a potentially deadly illness that was at the center of 2001 bioterror attacks.

FILE - In this Oct. 8, 2013, file photo, a sign ma
FILE - In this Oct. 8, 2013, file photo, a sign marks the entrance to the federal Centers for Disease Control and Prevention, in Atlanta, Georgia.

Researchers in the CDC's bioterrorism response lab are retracing the events within the lab between June 6 and June 13 that led to the possible exposure of 84 employees at the agency's Atlanta campus, an agency official told Reuters.

New details about the agency's investigation suggest the anthrax that was being inactivated in a high security lab may have been sitting in a bath of acid for 24 hours before being transferred to two lower-security labs.

What researchers are trying to find out is whether that was long enough to kill the anthrax, Dr. Paul Meechan, director of the CDC's environmental health and safety compliance office, told Reuters in a telephone interview.

“We don't know that, but we're doing experiments to prove it,” said Meechan. The CDC first disclosed the incident to Reuters a week ago.

An independent laboratory is running the same set of experiments to see if they get the same answers, which would add to the validity of the findings.

Meechan said workers in the bioterror lab were testing a new protocol for inactivating anthrax before sending the bacteria for experiments in two lower-security CDC labs.

The protocol they were following had been used by researchers at the CDC to inactivate other bacteria, but not on anthrax. It called for placing anthrax into a bath of acid for 10 minutes, removing some, putting it on a nutrient-rich plate and placing it in an incubator.

After 24 hours, the researchers checked to see if any colonies of anthrax had grown. None had, so the team took the anthrax that had been soaking in acid for 24 hours, put it on slides and sent it for testing in two other CDC labs.

The material from the 10-minute sample eventually germinated, started to divide and form a colony, a process that normally takes around 48 hours.

Why the team did not wait the standard 48 hours to be sure the acid bath had killed the bacteria is still under investigation, Meechan said.

Investigators want to learn what was happening to the anthrax cells left in the acid bath while the material from the 10-minute sample was in the incubator.

“We want to know whether or not in the 24 hours when they were waiting for that plate to grow, they were actually killing more of the anthrax, and possibly all of it,” Meechan said.

A CDC team is setting up an experiment using a similar setup, taking samples of anthrax soaking in acid at different time intervals up to 24 hours.

“The idea is to see how much time it takes to kill everything in that solution,” Meechan said.

The investigators' report is due to reach CDC director Dr. Thomas Frieden by early next week.