An investigation into a potentially dangerous blunder at a government lab found that a scientist kept silent about the accident and revealed it only after other employees noticed something fishy.
Officials on Friday released the results of an internal probe into the accident, which happened in January at the Centers for Disease Control and Prevention in Atlanta.
A deadly strain of bird flu was accidentally mixed with a tamer strain. The mix was sent to another CDC lab in Atlanta and to an outside lab in Athens, Georgia.
No one was sickened by bird flu. But unsuspecting scientists worked with the viral mix for months before it was discovered.
CDC officials have called this the most worrisome in a series of lab safety problems at the government agency.