A federal health official warned Tuesday that the deadly coronavirus could cause "severe" disruptions in the USA as global experts struggled to fend off the outbreak and avoid a pandemic.

Is it too late?

"Disruption to everyday life may be severe," Nancy Messonnier, director of the Centers for Disease Control and Prevention's National Center for Immunization and Respiratory Diseases, warned at a news conference Tuesday. Schools could be closed, mass public gatherings suspended and businesses forced to have employees work remotely, she said.

Messonnier said the coronavirus has caused sickness and death and sustained person-to-person transmission. That's two of the three factors for a pandemic, she said.

Stay up to date on coronavirus:Get USA TODAY's Daily Briefing in your inbox

“As community spread is detected in more and more countries, the world moves closer to meeting the third criteria – worldwide spread of the new virus,” Messonnier said.

Although the World Health Organization determined Monday that the term pandemic "did not fit the facts," experts said it very soon could.

Dennis Carroll, former director of the U.S. Agency for International Development's Global Health Security and Development Unit, credited China's "extraordinary control measures" with delaying the spread of the virus, but he said avoiding a pandemic is "very unlikely."

"The dramatic uptick of cases in South Korea, Iran and Italy are reflective of a self-sustaining spreading of the virus and a clear message that the horse is out of the barn," Carroll, who leads the Global Virome Project science cooperative, told USA TODAY.

Melissa Nolan, a medical doctor and professor of epidemiology at the University of South Carolina’s Arnold School of Public Health, cited new clusters in Iran, which faces at least 95 cases and has had 16 deaths, and Italy, which is dealing with 322 cases.

"If we continue to see focalized local transmission in areas outside of China, the WHO will need to reconvene," Nolan told USA TODAY on Tuesday. "We are very close to seeing this virus becoming a pandemic."

Nolan said responses to the outbreaks in Iran and Italy could help health officials in other countries prepare their own medical and quarantine policies before an outbreak. That is crucial, said Robert Glatter, an emergency physician at New York's Lenox Hill Hospital who fears the world is on the "cusp" of a pandemic.

"Trying to contain a disease which spreads like influenza, in this case COVID-19, is almost impossible," he said. "We are talking about rapid-fire and sustained transmission."

The global death toll from coronavirus rose to 2,762 on Tuesday night, with more than 81,000 confirmed cases.

That means redirecting the focus from containment measures to preparing for treatment of big numbers of sick patients with antivirals while continuing the effort to develop an effective vaccine, he said.

'An economic pandemic': The coronavirus becomes a bigger economic threat

Beyond an epidemic, which involves a defined region, a pandemic has global impact. It can be a moving target – there is no threshold, such as number of deaths or infections.

WHO, which could make a pandemic declaration, describes a pandemic as “an epidemic occurring worldwide, or over a very wide area, crossing international boundaries and usually affecting a large number of people.”

WHO Director-General Tedros Adhanom Ghebreyesus does not want to go there.

"I have spoken consistently about the need for facts, not fear,” Tedros said. “Using the word ‘pandemic’ now does not fit the facts, but it may certainly cause fear.”

Ogbonnaya Omenka, an assistant professor and public health specialist at Butler University's College of Pharmacy and Health Sciences, said he understands the concerns. The main implication of declaring a pandemic is requiring, or at least further urging, national governments to prepare facilities and health workers to treat a lot of patients, Omenka told USA TODAY.

"Not only is this costly, it may also trigger panic," he warned. "Countries may as well put in place these plans without the official announcement."

Tedros stressed that a pandemic declaration would not eliminate the need for health authorities to continue testing, limiting contact with the sick and encouraging frequent hand washing – the front-line defense.

Italy locks down 'hot spot' cities: WHO says coronavirus 'not yet' a pandemic

He noted that cases in China have declined for the past three weeks. In Wuhan, where health services were stretched when the outbreak began in December, the fatality rate is 2% to 4%. Elsewhere in China, it's less than 1%.

This season's flu death rate in the USA is less than 0.1%, according to the CDC. More than 30 million Americans have suffered from the flu this season, while the global number of confirmed coronavirus cases hasn't reached 100,000.

Thousands ill, many thousands recovered: Can you get coronavirus twice?

There is a vaccine for the flu. Labs around the world are scrambling to develop one for the coronavirus. President Donald Trump requested $2.5 billion to fight the virus, including more than $1 billion toward developing a vaccine. Some congressional Democrats said that may not be enough.

At a news conference Tuesday in India, Trump tried to tamp down concerns, saying the virus was "very well under control in our country." Confirmed cases totaled 57 Tuesday, and no one has died in the USA, although one American died in Wuhan.

"We have very few people with it, and ... the people are all getting better," Trump said. On Twitter, Trump added that the CDC and his administration were "doing a GREAT job" of handling the virus.

The president's tweet came shortly after the U.S. military confirmed its first infection, a solider based in South Korea. The 23-year-old man is in self quarantine at his off-base residence, the U.S. military said in a statement.

Messonnier acknowledged the CDC struck a more urgent tone in warnings about the virus in the USA. The proliferation of coronavirus in countries outside China raised the agency's expectations the virus will spread here.

"People are concerned about this situation – I would say rightfully so," Messonnier said. "But we are putting our concerns to work preparing. Now is the time for businesses, hospitals, communities, schools and everyday people to begin preparing as well."

Contributing: Steve Kiggins, USA TODAY; The Associated Press