The H5N1 flu incident, which the CDC discovered in the course of its post-anthrax investigation, entailed a relatively safe avian influenza being unintentionally contaminated at a CDC lab with a highly pathogenic H5N1 strain of influenza. On March 13 the CDC shipped that hazardous material to a facility operated by the Agriculture Department (USDA). Although the USDA lab in Atlanta was a high-level biosafety level 3 facility that required workers to shower in and out and wear respiratory protection, the lab was not supposed to have received that sample and did not have adequate clearance to handle that level of hazardous material. No workers are believed to have been exposed to the substance.