Federal health authorities said Tuesday they now expect a wider spread of the coronavirus in the U.S. and are preparing for a potential pandemic, though they remain unsure about how severe the health threat could be.

Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the Centers for Disease Control and Prevention, said Tuesday the agency expects a sustained transmission of the virus and called for businesses, schools and communities to brace themselves and plan for potential outbreaks.

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“We expect we will see community spread in this country,” meaning the virus circulating within local communities, said Dr. Messonnier. She added that the question isn’t if the virus will expand in the U.S., but when.

In the U.S., 14 locally diagnosed cases have been confirmed, with an additional 40 from the outbreak on the Diamond Princess cruise ship in Asia and three among Americans who returned from China aboard U.S.-chartered flights.

So far, American public-health systems have sought to contain the virus by isolating confirmed cases while monitoring close contacts of these patients for signs of infection. This strategy is most effective when the case count is relatively low and each case can be epidemiologically linked to each other and traced to an original source, health authorities say. That is the current situation with the confirmed U.S. cases.

But if the virus spreads more widely, it might become difficult or impossible to contain it with the current methods, experts say. Instead, the efforts would shift to strategies such as closing schools, canceling mass gatherings and requiring employees to work from home.

“The disruption to everyday life might be severe,” Dr. Messonnier said.

Meantime, the Trump administration’s response to the virus was challenged Tuesday in Congress. Health and Human Services Secretary Alex Azar, who heads the U.S. coronavirus task force, was questioned about whether his agency is doing enough, especially in light of its request for $2.5 billion in emergency funding—less than what was granted to fight earlier threats of pandemics.

“It seems to me at the outset that this request for the money…is lowballing it,” said Sen. Richard Shelby (R., Ala.), the committee’s chairman. “You can’t afford to do that.”

Democrats at the hearing pushed back on recent upbeat assurances about the virus by President Trump on Twitter. “We are disregarding scientific evidence and relying on tweets,” said Sen. Patty Murray (D., Wash.). “I’m deeply concerned we are way behind the eight ball on this.”



Mr. Trump this month said the coronavirus could go away with warm weather. But the CDC’s Dr. Messonnier said in a Feb. 12 media call that she would caution against “overinterpreting that hypothesis.”

Mr. Azar, who praised the president’s approach, said his agency is requesting the amount of funding that is needed, adding that the administration will work with traditional public-health tools to mitigate a sustained spread if it occurs.

Financial markets fell for the second day on concern about the virus’s economic impact, with the Dow Jones Industrial Average down nearly 900 points. As the markets slid, several administration officials appeared to temper the CDC’s comments about the virus.

Speaking at a media briefing, Mr. Azar said cases in the U.S. are contained and that “people shouldn’t panic when we see new cases.” He said Dr. Messonnier’s comments were aimed at educating the public about possible future actions. White House economic adviser Lawrence Kudlow, speaking on CNBC, said: “We have contained this. I won’t say airtight, but pretty close to airtight.”

Authorities have tested 426 people in the U.S. for the virus, not including those who have been repatriated. But many state and local health departments lack the test kits they need to diagnose the infections because federal health authorities are still working out kinks in the kits. The limited availability of the kits could hamstring local efforts to handle the anticipated rise in cases and identify cases that now exist, public-health and hospital officials said.

Testing for the virus has been relatively slow because most local health officials must ship patient samples to the CDC in Atlanta and isolate these patients while waiting for the results. That can take days. To speed up diagnoses, the CDC wants to send test kits to state and local health departments.

But the rollout stalled earlier this month after the kits produced inconclusive results during verification testing at state and local health departments.

© amanda voisard/Reuters “We still do not know when the CDC kit replacements will come out, and our members are pretty anxious about it,” said Scott Becker, chief executive officer of the Association of Public Health Laboratories. “It doesn’t feel like a good place to be.”

The CDC said it is working to remanufacture the reagent, the substance used in a chemical reaction in the tests, that is suspected to be at fault for the inconclusive results. Once that is done it will send out replacements.

Twelve states and localities are now testing for the virus themselves using kits determined to be effective. The CDC said it hopes commercial tests might be available soon to augment the CDC kit used by health departments and hospitals.

Tests are needed, especially if cases expand, because the symptoms of the coronavirus, such as a fever and a dry cough, are similar to those of the flu and other viral infections, said David Weber, medical director at the University of North Carolina Hospitals’ Departments of Hospital Epidemiology.

A delay in testing adds to the burdens of hospitals that need to keep patients while they wait for the results.

“U.S. hospitals are not set up to have a huge number of extra beds that are just sitting vacant, including those with quarantine capacity,” said Michael Mina, an associate medical director in clinical microbiology and pathology at Brigham and Women’s Hospital.

Write to Brianna Abbott at brianna.abbott@wsj.com and Stephanie Armour at stephanie.armour@wsj.com