The director of the Centers for Disease Control calls them "nightmare bacteria," and they're invading more hospitals and nursing homes.
Forty-two states are reporting problems with a class of super bugs known as carbapenem-resistant Enterobacteriaceae, or CRE.
Infections are not common but when they occur, they kill about half the people they infect. Plus, the infections spread their super-resistance to other bacteria.
The CDC hopes sounding the alarm now will stop CRE from moving out of hospitals and into communities.
More from the CDC: Patients face more lethal infections from CRE