Laboratories operated by the U.S. Centers for Disease Control and Prevention (CDC) have been under fire this year for their lapses in mishandling dangerous potentially lethal pathogens including anthrax and a deadly flu strain.

It appears, however, that CDC's series of mistakes that posed risks for some of its employees isn't over for this year. The Atlanta-based agency has yet again revealed on Wednesday that a CDC laboratory technician is currently under observation for possible exposure to Ebola virus, which has so far killed thousands in an unprecedented epidemic in Africa.

CDC said that the incident took place after a sample of the potentially lethal virus was erroneously transferred from a highly secure laboratory to a one with less secure protocols. The active Ebola virus samples appeared to have been mixed with specimens that were rendered inactive for testing in the lower security laboratory.

The mix-up was discovered on Tuesday after laboratory personnel realized that samples of the active virus material had been moved to the low-security lab. The material in question, however, was already destroyed before the mistake was identified.

The unnamed technician, who may have been exposed to the Ebola virus, was working in the second laboratory on Monday. A dozen other staffs are also being assessed after they entered the facility not knowing that possibly hazardous samples of the virus had been handled here.

CDC spokeswoman Barbara Reynolds said that the technician's risks of exposure are believed to be low even if the virus were active. The lab technician wore a gown and protective gloves at the time of the incident albeit without a face mask. In a laboratory setting, Ebola virus can be transmitted from a contaminated area through physical contact that spreads the virus to a person's eyes, nose or mouth.

Although the technician who handled the materials is being observed, he was not placed on quarantine. Reynolds said that the other employees who entered the facility where the potentially dangerous material was handled were assessed but none of them required monitoring.

CDC Director Tom Frieden expressed his concern over the incident and ordered a full review of all aspects of the incident.

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