April 17, 2015 -- Imagine being sick in the hospital with a bacterial infection and doctors can't stop it from spreading. This so-called "superbug" scenario is not science fiction. It's an urgent, worldwide worry that is prompting swift action.

Every year, about 2 million people get sick from a superbug, according to the CDC. About 23,000 die. Earlier this year, an outbreak of CRE (carbapenem-resistant enterobacteriaceae) linked to contaminated medical tools sickened 11 people at two Los-Angeles area hospitals. Two people died, and more than 200 others may have been exposed.

The White House recently released a comprehensive plan outlining steps to combat drug-resistant bacteria. The plan identifies three "urgent" and several "serious" threats. We asked infectious disease experts to explain what some of them are and when to worry.

### But First: What's a Superbug?

It's a term coined by the media to describe bacteria that cannot be killed using multiple antibiotics. "It resonates because it's scary," says Stephen Calderwood, MD, president of the Infectious Diseases Society of America. "But in fairness, there is no real definition."

Instead, doctors often use phrases like "multidrug-resistant bacteria." That's because a superbug isn't necessarily resistant to all antibiotics. It refers to bacteria that can't be treated using two or more, says Brian K. Coombes, PhD, of McMaster University in Ontario.

Any species of bacteria can turn into a superbug.

Misusing antibiotics (such as taking them when you don't need them or not finishing all of your medicine) is the "single leading factor" contributing to this problem, the CDC says. The concern is that eventually doctors will run out of antibiotics to treat them.

"What the public should know is that the more antibiotics you’ve taken, the higher your superbug risk," says Eric Biondi, MD, who runs a program to decrease unnecessary antibiotic use. "The more encounters you have with the hospital setting, the higher your superbug risk."

"Superbugs should be a concern to everyone," Coombes says. "Antibiotics are the foundation on which all modern medicine rests. Cancer chemotherapy, organ transplants, surgeries, and childbirth all rely on antibiotics to prevent infections. If you can't treat those, then we lose the medical advances we have made in the last 50 years."

Here are some of the growing superbug threats identified in the 2015 White House report.