For the U.S., it’s not if but when, federal officials say.

Americans should brace for the likelihood that the coronavirus will spread to communities in the United States, the Centers for Disease Control and Prevention warned Tuesday.

“It’s not so much of a question of if this will happen in this country any more but a question of when this will happen,” said Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases.

She said that public health officials have no idea whether the spread of the disease to the United States would be mild or severe, but that Americans should be ready for a significant disruption to their daily lives.

“We are asking the American public to prepare for the expectation that this might be bad,” Dr. Messonnier said.