A lab mix-up involving a deadly flu virus strain added to the Centers for Disease Control and Prevention 's public relations nightmare this summer . On Friday , the public health agency released the results of its internal investigation into the incident , along with a series of reports on actions being taken to ensure lab safety protocols are being properly followed . In May , CDC lab workers unintentionally mixed a low pathogenic , or non-dangerous , avian influenza virus sample with a potentially deadly virus called H5N1 , then shipped the sample to an external lab run by the U.S. Department of Agriculture . The H5N1 strain has killed millions of birds and infected more than 600 people over the last decade . But no one appears to have been at-risk of being infected during the incident since the sample was stored and shipped properly , according to the CDC reports . `` The contamination most likely happened due to the failure of a laboratory scientist to adhere to established best practices and the absence of an approved laboratory team-specific protocol for the work being done , '' the reports concluded . Dr. Tom Frieden , the CDC 's director , found out about the H5N1 incident nearly six weeks after it happened , something he called at the time `` most distressing . '' This delay in reporting the cross-contamination was due to `` a lack of awareness and understanding about reporting requirements for Select Agents , '' according to the reports . Around the same time he heard about the flu incident , Frieden was dealing with the possible exposure of up to 86 of his workers to anthrax . Anthrax investigation turns up 'distressing ' issues at CDC . Michael Farrell , who headed the Bioterrorism Rapid Response and Advanced Technology Laboratory involved , submitted his resignation in July . He had been reassigned from his post in June after the anthrax incident was made public . CDC lab director resigns after anthrax incident . The CDC says the potential anthrax exposure happened between June 6 and 13 . The bioterrorism lab had been preparing anthrax samples for use in two other labs on the CDC 's Atlanta campus and failed to deactivate the samples adequately . According to another CDC investigation report , the exposure happened because the lab did n't use an approved sterilization technique . It did n't have a written plan reviewed by senior staff to make sure all safety protocols were followed , and there was a limited knowledge of peer-reviewed literature about the process that would make it less dangerous . The lab also did not have a standard operating procedure that would make sure the transfer of the material would be safe . Bottom line : `` The scientists failed to follow a scientifically derived and reviewed protocol that would have assured the anthrax was deactivated , '' Frieden said last month . It `` should have happened , and it did n't . '' As a result of these problems , the CDC has stopped transferring materials in and out of its highest-level labs . `` The moratorium will remain in place pending lab-by-lab review of policies and procedures for laboratory safety and security , '' the CDC says . CDC 's lab problems have ripple effect on other outbreaks . Frieden plans to appoint a CDC director of laboratory safety , and establish a working group to review safety protocols . `` The work of safety is never complete , '' Dr. Michael Bell , interim director of laboratory safety , said in a statement . `` We will continue to take all necessary steps to maintain safety and advance CDC 's critical laboratory science work , so that CDC labs are the most scientifically rigorous and the safest in the world . ''
CDC lab workers unintentionally mixed non-dangerous flu strain with H5N1 . Reports : Contamination happened because scientists failed to follow `` best practices '' CDC director found out about cross-contamination several weeks after it happened .