It's an infection so severe it can kill and doctors say it's on the rise.
So why haven't most of us ever heard of it?
Diane Henry takes care of other people.
But for weeks last year, she could barely do anything.
"Started experiencing severe stomach pain, but ignored it," said Henry.
Finally her symptoms were so alarming, her mother forced her to go to the hospital.
"I had bloody diarrhea, weak, tired, just exhausted. I ended up staying there 30 days," said Henry.
Her recovery will last months longer.
"They removed five feet of my colon," Henry said.
Because of an infection called c diff.
Scientists have been in a pitched battle against c diff since discovering its effects thirty years ago.
Dr. Dale Gerding describes it as a bulletproof bug, because the toxic spores it releases can live on lab surfaces for six months.
And in just over a decade, c diff infections have risen dramatically, and become far more lethal.
"We have an epidemic strain circulating now. Patients are going into shock, they are unable to fight off the disease, they are dying precipitously," said Gerding an infectious disease specialist.
In the greatest of ironies, you're most likely to be infected if you've taken a medication that changed medical history and saved millions of lives.
That's because antibiotics attack bacteria indiscriminately, including the good kind that's so crucial to human health.
"In process of taking antibiotics you disrupt the normal protective bacteria in the gut. If that happens, and you ingest c diff, then c diff is able to establish itself," said Gerding.
Which is why Dr. Ken Lee will not prescribe antibiotics unless it's absolutely necessary.
Dr. Lee, who's also Diane's doctor, says outside of a hospital setting, c diff is still uncommon.
But he's seeing an increase in cases like Diane's.
For her, antibiotics were unavoidable because of chronic sinus infections.
But c diff experts say for millions of Americans who insist on antibiotics they're not helpful or necessary and patients shouldn't do it.
"The way to protect yourself as a patient, make sure you need really need the antibiotic," Gerding said.
Today, Diane Henry is learning how to eat again, without her large intestine.
She still respects the healing powers of antibiotics: but she says too few people know of their dark side.
"People need to understand there is a consequence, how dangerous they can be," Henry said.
But Dr. Dale Gerding says human trials will start this spring with a non-toxic strain of c-diff.