Shafaq News/ An American soldier in South Korea has tested positive for the new coronavirus, the U.S. military said on Wednesday.

The patient, a 23-year-old man, is based in Camp Carroll in Waegwan, only 12 miles from Daegu, the South Korean city at the center of an outbreak in the country. The New York Times said.

The soldier, the first U.S. service member to become infected, has been quarantined in his off-base residence, the military said.

The soldier visited Camp Walker, a military base in Daegu, on Monday and visited Camp Carroll from Friday to Tuesday.

South Korean and American “health professionals are actively conducting contact tracing to determine whether any others may have been exposed,” the military said.

The military added that it was “implementing all appropriate control measures to help control the spread of Covid-19 and remains at risk level ‘high’” for all its 28,500 soldiers stationed in South Korea “as a prudent measure to protect the force.”

Those measures include advising all troops to “limit non-mission essential” meetings and “off-installation travel.” At the gates of the American military bases across South Korea, stations have been set up to administer temperature checks and screening questionnaires.

On Tuesday, the United States and South Korea said they would consider scaling back joint military exercise after an outbreak among South Korean soldiers had infected at least 13.

South Korea reported 169 new patients on Wednesday, bringing the total number to 1,146, the biggest outbreak outside China. More than half of the patients were residents of Daegu.

Americans should brace for the likelihood that the coronavirus will spread to communities in the United States, the Centers for Disease Control and Prevention warned Tuesday.

“It’s not so much of a question of if this will happen in this country anymore but a question of when this will happen,” said Dr. Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases.

President Trump, in India, said that the United States was well able to protect itself against the spread of the coronavirus and offered an optimistic outlook.

“I think the whole situation will start working out,” Mr. Trump said during a news conference.

But his own health officials were not so upbeat. Dr. Messonnier said that public health officials have no idea whether the spread of the disease to the United States would be mild or severe, but that Americans should be ready for a significant disruption to their daily lives.

“We are asking the American public to prepare for the expectation that this might be bad,” Dr. Messonnier said.

The secretary of health and human services delivered an equally sobering message on Tuesday. The secretary, Alex M. Azar II, told a Senate committee, “This is an unprecedented, potentially severe health challenge globally.”

“We cannot hermetically seal off the United States to a virus,” Mr. Azar said. “And we need to be realistic about that.”

Federal and local health departments will need as many as 300 million masks for health care workers and additional ventilators for hospitals to prepare for a major outbreak of the coronavirus, he said. On Monday, the Trump administration requested $2.5 billion to help stop the spread of the virus.

Lawmakers from both parties made it clear they were unconvinced the Trump administration was prepared. When Senator John Kennedy, Republican of Louisiana, pressed for an exact number of people expected to be infected, the acting secretary of the Homeland Security Department, Chad F. Wolf, could not answer.

“I’m all for committees and task forces but you’re the secretary,” Mr. Kennedy responded. “I think you ought to know that answer.