But just wearing the gear isn't enough to avoid danger, according to health officials who suggested that contamination could have occurred while the health care worker was putting on or taking off the protective gear, which consists of a gown, a mask, gloves, a face shield, and booties.

"We don't know what occurred in the care of the patient in Dallas, but at some point there was a breach in protocol," said Thomas Frieden, director of the U.S. Centers for Disease Control and Prevention (CDC).

The Dallas health care worker's illness is a reminder of the risks medical personnel have faced during the Ebola outbreak that began in West Africa, and of how U.S. health officials have been scrambling to try