On Friday, the Centers for Disease Control and Prevention released the results of an investigation conducted after "potentially viable anthrax" was accidentally released at one of the agencies facilities in Atlanta, Georgia last month. The investigation described the situation as "serious" and found there were multiple other instances where dangerous pathogens were inadvertently released at CDC labs including one incident "earlier this year" involving a "highly pathogenic" H5N1 strain of bird flu that only came to light during the course of the investigation.

"I will say that I'm just astonished that this could have happened here," CDC Director Tom Frieden said at a press conference Friday announcing the results of the report.

According to the report, the anthrax was released after a scientist at the CDC's Bioterrorism Rapid Response and Advanced Technology (BRRAT) laboratory prepared extracts of eight "bacterial select agents" as part of an experiment to evaluate a potentially faster way to detect anthrax. The samples used in the lab were believed to be sterile after being treated and observed for 24 hours and were subsequently moved to a lower security lab. On June 13, the report said a CDC scientist noticed "unexpected growth on the anthrax sterility plate" that indicated "the B. anthracis sample extract may not have been sterile when transferred."

The investigation determined it was "extremely unlikely" CDC staff were exposed to anthrax, however, it was "not impossible." Multiple staff members were taken to the emergency room for treatment and the report said, as of July 10, "no staff members are believed to have become ill with anthrax." Still, the report found the situation was "serious."

"This was a serious event that should not have happened," said the report. "Though it now appears that the risk to any individual was either non-existent or very small, the issues raised by this event are important."

Additionally, the report noted the "CDC is aware of four other such incidents in the past decade" including the bird flu contamination, which investigators said they were "made aware" of "as this report was being finalized." According to CNN, Frieden said the bird flu contamination occurred six weeks ago and the "most distressing" aspect of the situation was that he learned of it "less than 48 hours ago."

The report also described what went wrong when the anthrax was released. Specifically, the report described "the lack of an approved, written study plan" for the anthrax research project as "the overriding factor contributing to this incident." It also identified other factors that led to the anthrax release including; "use of unapproved sterilization techniques," "transfer of material not confirmed to be inactive," "inadequate knowledge of the peer-reviewed literature," "lack of a standard operating procedure or process," and use of pathogenic anthrax "when non-pathogenic strains would have been appropriate for this experiment."

Going forward, the report said the CDC would take several steps to prevent similar incidents in the future.

"CDC has concrete actions underway now to change processes that allowed this to happen, and we will do everything possible to prevent a future occurrence such as this in any CDC laboratory, and to apply the lessons learned to other laboratories across the United States," the report said.

These measures will include establishing "clear, proven procedures ... for inactivation and non-viability testing of all types of materials that may be produced by the laboratories," internal reviews, creating a "lead laboratory science position to be the CDC-wide single point of accountability for laboratory safety," and creating an "external advisory committee to provide ongoing advice and direction for laboratory quality and safety." The report also identified changes the CDC will make at the BRRAT laboratory where the anthrax release occurred. According to the report, the BRRAT lab has been closed since June 16 and will not be reopened until an "assessment and appropriate follow-up actions" have occurred. The report also said "appropriate personnel action will be taken with respect to individuals who contributed to or were in a position to prevent this incident."