“We have to rethink the way we address Ebola infection control because even a single infection is unacceptable,” CDC Director Tom Frieden told reporters, detailing the response effort after an unidentified nurse was diagnosed with Ebola over the weekend.

“It doesn’t change the fact that we know how Ebola spreads,” Frieden said of the first known transmission in the United States. “It does change, substantially, how we approach it.”

The nurse who contracted the disease tested positive for Ebola after attempting to treat Thomas Eric Duncan, the Liberian national who died from the virus after traveling to the United States.