"This disease can be fatal over a long period of time," said Dr. Gwen Huitt of the National Jewish Medical and Research Center in Denver.
Doctors don't know how it is spread, but they do have some frightening theories, reports CBS News Correspondent Bobbi Harley.
"When we take our morning shower, we are creating a mist that is just the right particle size to breathe into our lungs," infectious disease specialist Huitt said.
The bacteria has always been in water and soil. Recently it's been showing up in people primarily in the southeastern United States and most often striking thin, white women. But it's so frequently misdiagnosed as pneumonia or bronchitis, researchers have no clear idea how many have been affected.
"Where are we...what is this? We're not so sure and that is, for doctors, a very uncomfortable place to be," said Dr. David Ashkin, medical executive director of the A.G. Holley Hospital in Florida, and the state's former tuberculosis director.
"I was coughing and coughing and sick, then I got pneumonia again and I was treated again and...I just kept getting sicker and sicker," remembers patient Fern Leitman.
The bacteria ate away at her lungs, forcing her to undergo intense drug and physical therapy just to stay alive.
Doctors call it an epidemic in slow motion. While it most often infects people who are more susceptible to respiratory infections, the disease's progression has been helped along by behavioral changes in the last few decades.
Showers have replaced baths and enclosed shower stalls have taken over where tubs and curtains once prevailed. That's making it easier for the bacteria to get into people's lungs.
Add to that reduced temperatures in home water heaters to conserve energy and plastic pipes instead of copper ones, and an ideal bacteria breeding ground has been created.
Zelda Rosenthal was lucky. After two years of therapy, she is now disease-free, but still cautious.
"I do take showers, I still take showers, but I don't stay in there very long," she said.
Fern Leitman doesn't take them at all any more.