Today, the scar on Tanya's upper body reminds her that she's lucky to be alive. Since doctors had to remove almost 9 pounds of flesh and muscle to rid her body of the bacteria, Tanya is left with nothing more than a thin layer of skin to protect her rib cage and right lung. "It's very fragile," she says. "Even a pinprick could go right into my lung or something, and I could die."

Watch as Tanya talks about life after amputation.

How did a small cut do so much damage in less than three days? Dr. Oz says necrotizing fasciitis burrows into the muscle and liquefies the surrounding tissue. "That's why it's called the flesh-eating bacteria—because it literally takes away the inside of your body," Dr. Oz says. "On the outside when you look at it, it doesn't look any different."

As the bacteria eat away at a person's flesh, Dr. Oz says toxins are released, which can destroy the lungs and kidneys and cause the body to shut down.