WASHINGTON >> As thousands of Americans flee from Europe and other centers of the coronavirus outbreak, many travelers are reporting no health screenings upon departure and few impediments at U.S. airports beyond a welcome home greeting.

Since January, officers from Customs and Border Protection have been on heightened alert for travelers who could potentially spread the virus. The Department of Homeland Security has told employees to look for visible physical symptoms and search through their travel documents and a federal database that tracks where they came from. Those customs officers will soon have to spot symptoms among a flood of more Americans funneled to designated airports from multiple countries in Europe, an administration official said, after President Donald Trump announced new travel restrictions on the region this week.

But travelers, including some who say they showed visible signs of illness, say screening has been lax. Members of Congress this week grilled senior officials from Homeland Security over what some described as a porous screening process. And customs officers at airports question how accurately they can pinpoint people with symptoms and what safeguards are being taken to protect their health.

Even top officials at the department acknowledge the task of sealing the United States from the virus is impossible.

“This has never been from Day 1 intended to be a hermetically sealed process,” said Kenneth Cuccinelli, the acting deputy secretary. “We are trying to reduce and delay the biggest peak in the virus wave hitting on the United States of America. And all of these steps reduce and delay. They do not stop of the virus.”

“Viruses do not care about boundaries,” he said.

Maggie McDow, 46, said she had swollen glands when she landed at Dulles International Airport outside Washington, one of 11 airports where travelers who have recently been in China or Iran are being funneled. McDow had flown from London, but before that, she had stopped in South Korea, a coronavirus hot spot.

McDow said she heard plenty of instructions from airport officials for those feeling ill in airports abroad. But when she reached the United States, she said, “There was none of that.” A customs officer stamped her passport, and she was on her way.

“No one asked where I had traveled. I guess they just assumed we all were just coming from London and so no big deal,” McDow wrote in an email because she was too sick to speak on the phone and has yet to be tested for the coronavirus. “I could have been coughing and feverish, and it seemed no one would have batted an eye.”

The Trump administration has barred entry to foreigners who in the past 14 days have visited China, Iran, and beginning at 11:59 p.m. Friday, 26 countries in the European Union. The administration has also told customs officers to use the federal travel database, documents and interviews with travelers to determine who to refer to a health screening at the airport. Officers are also required to refer those with symptoms coming from South Korea or Italy to be screened by the Centers for Disease Control and Prevention, according to Stephanie Malin, a spokeswoman for Customs and Border Protection.

Malin said that as of March 4, more than 63,000 travelers at airports, seaports and the land border had been referred by a Customs and Border Protection officer for a health screening. Cuccinelli said last week at a Senate homeland security hearing that the screenings had been successful at slowing the outbreak.

“It bought us time,” Cuccinelli said.

The crush of Americans returning from Europe will make those screenings that much harder.

Tony Reardon, the president of the National Treasury Employees Union, which represents officers from the section of Customs and Border Protection that conducts screening at U.S. airports, said officers were concerned about travelers not being truthful, or not knowing, about their symptoms.

“They are worried about the imprecise distinctions on when travelers may be contagious,” Reardon said. “They are also worried about whether all passengers who are at risk based on their travel history are being properly flagged for screening.”

“CBP’s highest priority is the health and safety of our employees and their families and we are taking every available precaution to protect our workforce,” said Nathan Peeters, a spokesman for the agency.

Three security screeners with the Transportation Security Administration at a Northern California airport have tested positive for the coronavirus, the agency said this week. Two medical contractors employed by Homeland Security also learned last week that they had the virus. The department closed a field office in Washington State for two weeks this month after an employee contracted the disease.

“They are caught in the middle,” said Gil Kerlikowske, the former commissioner of Customs and Border Protection, said of officers at the agency. “You’re depending on them to do a host of things.”

He said that if travelers returned without being screened, it was because federal agencies had given customs officers vague instructions.

Lawmakers have also shared those concerns.

Sen. Dick Durbin, D-Ill., sent a letter to the CDC demanding it clarify what airport screening was being given to travelers coming from South Korea and Italy. He highlighted two passengers returning from Italy who had not been screened in Chicago but later tested positive for the coronavirus.

At a House homeland security committee hearing this week, Rep. Sheila Jackson Lee, D-Texas, told Cuccinelli that those arriving in Texas on connecting flights from Italy did not receive adequate screening.

“CBP is not prepared,” Jackson Lee said. “You need to implement some sort of testing for CBP in terms of asking the question of whether or not the person has come from Italy, period.”

Malin said governments in Italy and South Korea were screening travelers bound for the United State before their departures.

William Yates, 28, said that did not happen to him. He did not undergo any medical screening before he left Rome, with a layover in London, or before boarding his flight from London to Phoenix. While he experienced no symptoms, he believed he might be stopped since he visited Emilia-Romagna, a region in Italy where provinces have been locked down because of the outbreak.

When he arrived in Phoenix, he was asked only if he had visited Milan.

“‘Cool, welcome back.’ And that was it,” Yates said.

He is currently working from home as a precaution. A supervisor in an emergency room, Yates did not want to risk spreading any illness to other patients.

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