The new case shows a breach in infection control and reveals that even in the United States, with the best conditions and protective gear available, mistakes can happen that expose more people to Ebola.

The health worker had been caring for a Liberian man who died of Ebola Wednesday at Texas Health Presbyterian Hospital.

Federal officials have said that all hospitals must be prepared to rapidly diagnose and isolate any Ebola cases that turn up. Transferring such a patient to one of the specialized units set up to deal with high-risk germs carries a risk that others could be exposed.