By Alexandra Sifferlin

Hospitals across the United States need to increasingly “think Ebola” while the outbreak in West Africa is ongoing, a top health official said Monday, one day after a second diagnosis in the U.S. was confirmed.

“Stopping Ebola is hard, but we are working together to make it easier,” Tom Frieden, the director of the Centers for Disease Control and Prevention, said during a news conference. “Even a single infection is unacceptable.”

Frieden said the health agency has doubled down in Dallas with an even larger team on the ground, helping to track down all health care workers who cared for the first Ebola patient and reiterating the importance of meticulousness in processes like getting in and out of personal protective equipment. Thomas Eric Duncan, who arrived from Liberia on Sept. 20, died last week. A nurse who treated him, identified as Nina Pham, 26, was confirmed Sunday to have Ebola.

Frieden insisted his words were misunderstood on Sunday, when he said there was a “breach in protocol,” and that he wasn’t pointing fingers. “People on the frontlines are protecting us. The enemy here is Ebola, not a person, not a hospital,” he said. “We need to all take responsibility for improving the safety on the front lines. I feel awful a health care worker was infected.”

The CDC told TIME that it will continue over the next days and weeks to press importance of its recommendations for hospitals to be prepared for Ebola, and maintain its offering of webinars and trainings for health workers as well as support for hospitals. One new recommendation is that hospitals have a lead person in charge of making sure procedures are followed carefully.