CDC Lab Workers May Have Been Exposed to Ebola

— -- Lab workers at the Centers for Disease Control and Prevention's Atlanta headquarters were possibly exposed to material that "may have contained" live Ebola virus, the agency reported.

What workers thought was a virus that was not alive was on a sealed plate as it was transferred from a high-level biosafety lab to a lower level lab, according to a CDC statement. They discovered Tuesday that the virus may have been alive.

The agency "cannot rule out the possible exposure" of one of the lab technicians, the statement reads. This technician had no symptoms and will be monitored for 21 days.

"I am troubled by this incident in our Ebola research laboratory in Atlanta," CDC Director Dr. Tom Frieden said in a statement.

Additional employees who entered the lab will also be assessed, the statement reads, but it doesn't say how many.

CDC workers reported the incident to leadership "within an hour" of its discovery, according to the statement. The CDC is conducting an internal investigation.

"Thousands of laboratory scientists in more than 150 labs throughout CDC have taken extraordinary steps in recent months to improve safety," Frieden said. "No risk to staff is acceptable, and our efforts to improve lab safety are essential -- the safety of our employees is our highest priority."