CNN  — 

One of the top officials at the Centers for Disease Control and Prevention warned Americans on Tuesday that health experts foresee the novel coronavirus that has killed thousands spreading in the United States.

“We expect we will see community spread in this country,” said Dr. Nancy Messonnier, director of the CDC’s National Center for Immunization and Respiratory Diseases. “It’s not so much a question of if this will happen anymore, but rather more a question of exactly when this will happen and how many people in this country will have severe illness.”

The agency tweeted Tuesday evening that Americans should think about getting ready.

“Now is the time for US businesses, hospitals, and communities to begin preparing for the possible spread of #COVID19,” it wrote, referring to the name the World Health Organization has given the novel coronavirus. “CDC continues to work with business, education & healthcare sectors, encouraging employers to be prepared.”

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Messonnier said her agency wants people to understand their lives might be disrupted.

“We are asking the American public to work with us to prepare in the expectation that this could be bad,” she said.

She said CDC officials have been saying for weeks that while they hope the spread won’t be severe in the United States, they are planning as if it could be.

“The data over the last week, and the spread in other countries, has certainly raised our level of concern and raised our level of expectation” of community spread, she said.

The CDC still doesn’t know what that will look like, she added. Community spread could be reasonably mild or very severe.

Americans should also talk to employers about working online and talk to doctor’s offices about telehealth, the CDC says.

Messonnier said she talked her family and told them that while they are not at risk right now, they should plan for what to do if their lives were significanl