At the height of the Ebola epidemic in West Africa five years ago, federal health officials faced what seemed like an impossible request: Could U.S. airports screen passengers for the deadly virus when they arrived from three hard-hit nations, Guinea, Liberia and Sierra Leone?

“We didn’t know it was possible,” said Tom Frieden, then-director of the Centers for Disease Control and Prevention. “The Department of Homeland Security said, ‘Actually, we can help you with that.’ ”

That brainstorming session in the White House Situation Room created a tool critical to limiting another emerging threat, coronavirus, which has sickened more than 6,000 and killed at least 133 in China.

Public health officials are racing to halt the spread of the mysterious virus, identified last month in the country’s central city of Wuhan, so it does not proliferate in the USA. With no vaccine, officials rely on public health tools of identifying, testing and isolating people sickened with the respiratory virus to prevent its spread.

Only five U.S. travelers returning from Wuhan, the epicenter of the outbreak, have been confirmed with the virus. An additional 110 people are under investigation for the virus. It has not spread from person to person on U.S. soil.

The health risk to Americans remains low, and the CDC’s goal is to prevent sustained, person-to-person spread of the virus, said agency Director Robert Redfield.

Still, the CDC and other experts warn more cases are likely to emerge nationwide as the virus accelerates in China and gains a foothold in a growing number of countries.

“It is predictable we will face new microbial threats,” said Frieden, who heads a group called Resolve to Save Lives. “Although we are much better prepared than we were 17 years ago when SARS emerged, we are still nowhere near as prepared as we need to be.”

‘Broader than we suspect’

Federal, state and local officials have worked to prepare for a deadly global threat for the past two decades and learned from scares such as the anthrax mailings in 2001, severe acute respiratory syndrome, or SARS, in 2003 and the Ebola outbreak in 2014. More recently, coordinated efforts quashed outbreaks of mosquito-borne Zika virus in 2015 and the measles last year.

“After the Ebola outbreak, the United States has really fortified itself against high-consequence infectious diseases,” said Amesh Adalja, senior scholar at Johns Hopkins Center for Health Security. “This is the payoff. Thus far, we have a well-contained group of five patients.”

Adalja said it’s difficult to gauge how lethal a virus is when cases first emerge. The number of deaths might initially seem higher because people seek care when they are sick or their condition worsens because of underlying health conditions. But as more people are diagnosed with mild cases, the death rate will probably go down. The death rate for the new illness trends much lower than for comparable coronaviruses SARS and MERS.

All U.S. cases linked to the outbreak among travelers returning from Wuhan have been described as mild.

“You are going to get a detection bias to pick up more severe cases first,” Adalja said. “As time evolves, you will see more of the mild cases. That’s why it’s very hard to trust some of the numbers in the beginning when you are looking at fatality rates.”

Experts underscore the importance of quickly identifying new threats. Options are limited should a new virus, such as coronavirus, proliferate in an unprotected population. Chief among weaknesses are global blind spots, mainly developing countries in Africa and Asia, where disease can spread for weeks or months before officials can recognize and take steps to control outbreaks, Frieden said.

China responded to the coronavirus faster than it did to SARS nearly two decades ago. Last month, officials announced the discovery of the virus, rapidly sequenced its genome and shared the information with health officials worldwide. That allowed the CDC and its global counterparts to develop a test to detect the virus, and it kickstarted the National Institutes of Health’s effort to develop a vaccine.

The virus may have spread before Chinese officials publicly disclosed its existence, some said.

“It’s probably broader than we suspect,” Adalja said. “I suspect this virus had been transmitting for some time before it was recognized. And it has settled itself into the community of Wuhan, which is why we are seeing these numbers go up.”

James Hodge, professor of law at the Sandra Day O’Connor College of Law and director of Arizona State University’s Center for Public Health Law and Policy, cautioned that although the coronavirus may not be more deadly than the common flu, there is no vaccine, known treatment or cure.

“Any time we are dealing with an unknown condition that could strike and kill within a two-week period of time, that’s serious,” Hodge said. “We are seeing something that has gotten U.S. and international attention for good reasons. Panic time? No. But reason to be concerned? Yes, absolutely.”

William Haseltine, an infectious disease and drug development expert and president of the global health think tank ACCESS Health International, said a coast-to-coast outbreak is not unfathomable.

“We’re definitely not ready. This virus can spread, and it can be deadly,” said Haseltine, who headed research on an anthrax antidote. “We’ve prepared for bioterrorism in general. We haven’t prepared for coronavirus as a potential threat specifically.”

CDC’s role in global coronavirus

Health and Human Services Secretary Alex Azar urged China to welcome a team of U.S. public health experts and scientists to gather basic information about the virus. Among the questions: How long can a person be infected without showing symptoms? How does the virus spread?

China reported people without symptoms can spread the virus, but U.S. scientists aren’t convinced. Other coronaviruses spread when an infected person has symptoms such as fever and coughing. U.S. heath officials urged the public to practice standard flu-prevention strategies: Wash your hands, cover your mouth when sneezing or coughing and stay home from work or school when ill.

The World Health Organization announced Tuesday it would send a group of international experts to China to better understand the outbreak and guide global response efforts.

“More cooperation and transparency are the most important steps you can take toward a more effective response,” Azar said at a news conference Tuesday.

Such global cooperation is critical to help stop the spread of infectious diseases, said William Schaffner, a Vanderbilt University School of Medicine professor of preventive medicine.

For years, Schaffner said, the CDC has employed disease detectives in developing countries to improve its capacity to detect and investigate diseases.

“We have two goals in this – one is humanitarian. We want to help as many people as possible,” he said. “The other is serious self-interest. If we can confine the problem at its source, it won’t come here.”

Congressional funding to improve global health security can vary from year to year. A Kaiser Family Foundation analysis found spending ranged from $400 million to $500 million but surged to $1.34 billion after the Ebola outbreak. That money supported a five-year effort to help developing countries detect, respond to and prevent health threats.

China and the CDC have a 20-year partnership that has vastly improved the nation’s ability to respond to outbreaks such as the coronavirus, Frieden said. Cuts to the global health program might jeopardize long-term progress.

“Public health isn’t a competition,” Frieden said. “We have a common enemy – dangerous microbes.”

Federal, state and local health officials have refined efforts to reduce disease risk among travelers.

The CDC and HHS said Tuesday they would expand screening to 20 airports, up from five. Airport screening consists of two noninvasive measures – temperature checks and questionnaires. The CDC issued a level three travel warning advising against all nonessential travel.

Leila Barraza,an assistant professor of public health law at the University of Arizona and co-author of a study on airport public health preparedness in 2018, said it’s not clear how fast symptoms appear.

“There’s been research as to whether someone’s temperature would really change on one flight – how fast the symptoms would occur,” she said.

Barraza said travelers may be referred to a hospital for further evaluation if they traveled in an affected area or were in contact with someone who might be infected. Even if a passenger doesn’t have symptoms, screenings are helpful for educational purposes, she said.

“If they can identify even one case, that can be extremely helpful in preventing that person from exposing further individuals,” she said.

Hospitals are accustomed to treating people during a busy flu season. Some are beginning to ask patients whether they traveled to China. The question is important because symptoms of coronavirus – runny nose, headache and cough – are similar to those of the common flu and other respiratory viruses.