“They kept adding more protective equipment as the patient [Duncan] deteriorated. They had masks first, then face shields, then the positive-pressure respirator. They added a second pair of gloves,” said Pierre Rollin, a CDC epidemiologist.

Despite the infection-control efforts, a nurse, Nina Pham, 26, somehow contracted Ebola at Texas Health Presbyterian Hospital Dallas while caring for Duncan, a Liberian man who flew to the United States last month. Pham is being treated at the same hospital, and Tuesday she was reported to be in good condition. (On Wednesday, state officials announced that a second worker who cared for Duncan had also tested positive for the virus.)