We begin with that scare playing out in Atlanta tonight, the CDC asking how could this happen, one of their own workers making a huge and dangerous mistake, potentially exposing his co-workers to live... See More
We begin with that scare playing out in Atlanta tonight, the CDC asking how could this happen, one of their own workers making a huge and dangerous mistake, potentially exposing his co-workers to live anthrax. Here's the latest at this hour. We're learning 75 CDC employees may have been exposed, those workers being treated at this hour. Tonight there's now an investigate under way into how this happened. ABC's chief medical editor, Dr. Richard Besser who spent many years at the CDC got the call today, his source in the lab telling him he was, quote, devastated. So he lead off with Dr. Besser. Reporter: The CDC is telling us tonight that something went terribly wrong. Live anthrax was passed along to labs that weren't equipped to handle it. Between June 6th and 13th, 75 people without the needed protective gear may have breathed it and become infrequented. The bio labs at the CDC in Atlanta handle the deadliest diseases and viruses in the world. From E bowl la to smallpox where precautions are serious and necessary. This is where scientists and doctors work on such deadly diseases as plague and west nile, T.B. And HIV. Tonight the labs are shut down, sealed, being decon tomorrow natd. It's that live form of anthrax that got, somehow, into lower level labs. There's no risk of these 75 workers spreading the disease to others, friends or family, because it isn't spread person to person. There is real concern for the workers themselves. None of the workers show any symptoms yet but they're not yet in the clear. Symptoms like fever and chills, shortness of breath, confusion, dizziness and headache. If anthrax goes untreated, it has a very high mortality rate, about 85%. Even if you get the right antibiotics for it, there's a 40% mortality rate. These workers are all being offered antibiotics for 60 days, and the vaccine just in case. For an organization that works so often with the deadliest diseases on the planet, it's a frightening mistake. Dr. Besser is with us now. You made the point that it's only these workers, not their families, not their neighbors. Why is that? You have to breathe it in to get sick. Rarely you can get it from contaminated clothing. I learned that the outer clothes were left in the lab. But they are concerned about the workers. Yeah. This can live in your body for 60 days and infrequent you and it can be deadly. 60 days of antibiotics, plus a vaccine. The bigger picture, people are going to say this is one of the most dangerous labs in the country. How does a mistake like this happen? This is one of the world's premiere labs. I spoke with them and they are absolutely devastated. They're going to look to see how did this happen and I think there are going to be some outside eyes looking at this as well.
This transcript has been automatically generated and may not be 100% accurate.