The Centers for Disease Control and Prevention (CDC) shut down two of its research labs on Friday after a serious anthrax scare and a safety problem involving deadly bird flu.
The agency also revealed on Friday a previously undisclosed accident with a dangerous H5N1 bird flu strain at one of its labs.
In June, the agency revealed that as many as 75 CDC employees in Atlanta were potentially exposed to live anthrax bacteria sent to labs unequipped to handle dangerous pathogens.
Besides these back-to-back accidents, the agency also announced that two of the six decades-old vials containing smallpox virus recently discovered in Maryland contained live viruses capable of infecting humans.
Thomas Frieden, director of CDC, said these events showed "completely unacceptable behavior" and said the world needed to reduce the number of labs handling dangerous agents.
Tasneem Nashrulla is a reporter for BuzzFeed News and is based in New York.