The federal government is mobilizing to try to stop the spread of a deadly superbug that can’t be killed by antibiotics and was found in the U.S. for the first time.

The Centers for Disease Control and Prevention said Tuesday it is working with the Department of Defense and local health agencies to identify people who may have come into contact with a Pennsylvania woman who came down with the version of E. coli. No other cases have been identified in Pennsylvania or in other parts of the U.S.