Lab workers at the Centers for Disease Control and Prevention shirked safety protocols for handling anthrax last week, possibly exposing as many as 84 people to the deadly bacterial spores, Reuters reported Saturday.

News broke on Thursday that scores of CDC employees in Atlanta had been exposed to live anthrax, the white powdery pathogen infamous for killing five people in the 2001 postal service attacks. A high-security CDC lab had been preparing the spores earlier this month for lower-security laboratories to conduct counter-bioterrorism research. They were supposed to ensure that the bacteria were dead before transporting them, but did not.

CDC investigators have so far learned that workers in the high-security lab didn't follow a protocol requiring scientists to monitor the spores for 48 hours to make sure they are dead. Instead, the workers waited only 24 hours, Reuters learned. The AFP news service has reported that the number of people exposed to the live spores could be 84 or more, and could rise "as more come forward," CDC spokesman Tom Skinner told reporters there. While no one has died or gotten sick, everyone who went near the spores were treated with antibiotics and vaccines.

This was perhaps the largest security breach ever at a U.S. biohazard facility. At least two people are likely to be implicated in the breach, because at least two people are required to handle anthrax, per CDC regulations. That rule — like the Air Force two-man rule requiring two people to turn the nuclear launch key — is to prevent rogue workers from smuggling biological weapons, and to discourage safety breaches, like this one. While many have praised the CDC's record to date, Skinner, the agency's spokesman, said the investigation's results will likely lead to new safety measures.