Health officials reported the first U.S. case of person-to-person transmission of the new coronavirus Thursday as the World Health Organization set in motion a global effort to fight the outbreak by declaring it a public health emergency.

Late Thursday, the State Department also issued a “do not travel” advisory for China. That warning level — the department’s highest — had previously been in force only for the province where the outbreak began.

State and federal officials said the sixth infected person in the United States is married to the Chicago-area woman who contracted the virus when she traveled to Wuhan, China, the epicenter of the outbreak. The unidentified man, who is in his 60s, has been isolated in the same suburban hospital as his wife since Tuesday, when he began exhibiting symptoms consistent with the early stages of the virus, including fever, coughing and shortness of breath, officials said.

Officials suspect he picked up the virus in the couple’s home while his wife was symptomatic, according to Jennifer Layden, state epidemiologist for the Illinois Department of Public Health. The woman, who was identified last week as the second U.S. case, has been hospitalized since and is doing well, Layden said.

Her husband has not attended mass gatherings, Ngozi Ezike, director of the state health department, said in a news briefing. “The virus is not spreading widely across the community,” she added.

Officials are tracing the people who came in contact with the new patient but are not recommending any new precautions by others, Ezike said.

Around the globe, however, and particularly in China, the respiratory illness caused by the newly identified virus continued on a widening, destructive path that increased public anxiety. The virus had killed 213 people — all of them in China — and infected more than 9,700 as of Friday.

About 90 cases have been recorded outside China — including the first two in Italy, both Chinese tourists, according to news reports.

Airlines are cutting or completely canceling flights to China, a nation of 1.4 billion people, and some businesses have begun preparing for a possibly extended slowdown in operations and sales there. The union representing 15,000 American Airlines pilots sued the company to halt the carrier’s U.S.-China service, citing “serious, and in many ways still unknown, health threats posed by the coronavirus.”

The WHO criticized such actions, urging countries against imposition of trade or travel barriers. It also called for the world community to combat misinformation about the outbreak and accelerate vaccine development.

The global health agency urged Chinese health authorities to take a range of measures, in addition to the travel restrictions already imposed on 50 million people in central China’s Hubei province.

It asked China to collaborate with the WHO and others to conduct investigations; share full data on all of its cases; keep people informed about the evolution of the outbreak and protection measures the government has taken; boost efforts to identify the animal source of the outbreak; and conduct exit screening at international airports and ports so travelers with symptoms can be identified and treated.

The WHO cannot enforce its recommendations, but countries are under political pressure to follow them.

Public health officials and experts have criticized China for not sharing crucial data about patients, including when they became ill. That information is needed to learn more about the evolution of the outbreak, which would help officials control its spread.

WHO Director-General Tedros Adhanom Ghebreyesus nevertheless praised China’s efforts to contain the outbreak.

“Let me be clear: This declaration is not a vote of no confidence in China,” he said. “On the contrary, WHO continues to have confidence in China’s capacity to control the outbreak. The Chinese government is to be congratulated for the extraordinary measures it has taken to control the outbreak despite the severe social and economic impact those measures are having on the Chinese people.”

The White House also announced the formation of a task force, led by Health and Human Services Secretary Alex Azar, to coordinate the U.S. response.

As countries began repatriating citizens or planning to do so, the difficult task of balancing personal rights and public protection became more acute. In Southern California, Riverside County health officials issued a “quarantine order” Thursday that allowed them to hold an individual against the person’s will.

The person, who had been flown in from Wuhan a day earlier, had attempted to leave the military base where 195 American evacuees are being temporarily held for monitoring and observation.

“They expressed a desire to leave, they tried to leave,” said Jose Arballo Jr., a spokesman for Riverside County’s Department of Public Health. “But they never got off the grounds of the base.”

In a statement, officials said Cameron Kaiser, the county’s public health officer, ordered the person to stay on the base until the individual is cleared by health officials, because of “the unknown risk to the public should someone leave [the base] without undergoing a full health evaluation.”

“The individual will remain at [the base] until their health status is confirmed,” the statement said. “All other passengers from the flight also remain at [the base] and continue to be evaluated.”

In Australia, Prime Minister Scott Morrison’s plan to send evacuees from Hubei to Christmas Island, a territory 1,000 miles offshore, drew mixed reaction. There are hundreds of Australian citizens in the Chinese province.

If Australia is able to bring them home, they will be required to stay on the island for two weeks and pay about $677 each for the evacuation, Australian media reported.

In a television interview with the Australian Broadcasting Corp., Daniel Ouyang, an Australian citizen stuck in Wuhan after visiting family, said he is debating whether he should board a flight that will require the stay on Christmas Island.

“What’s going to happen to us when we arrive?” he asked. “What’s going to happen to our freedom? What are going to be able to do and not be allowed to do?”

In Chicago, Public Health Commissioner Allison Arwady said the new U.S. patient was placed in isolation Tuesday, the same day he exhibited symptoms. The man, who has underlying health conditions, is in stable condition at a medical center in Hoffman Estates, a suburb of Chicago, where his wife is also hospitalized.

Arwady said the man has “been extremely helpful” in sharing the details of his recent activities.

“He has not taken the ‘L.’ He has not attended any large gatherings,” she said, noting that he has used his own car, not the city’s elevated-train system, to get around. “This news does not change the risk to the general public. It is not a local emergency.”

Officials warned a jittery public, however, to expect additional cases and perhaps more person-to-person transmissions of the virus. That has now occurred in the United States, Germany, Japan, Vietnam, China and Taiwan.

“Moving forward, we can expect to see more cases, and more cases means the potential for more person-to-person spread,” said Nancy Messonnier, director of the National Center for Immunization and Respiratory Diseases at the U.S. Centers for Disease Control and Prevention.

Nonetheless, the overall risk to people in the United States is still considered quite low, officials said. They advised U.S. residents to take the kinds of precautions they would to guard against seasonal flu — which already has killed at least 8,200 people in late 2019 and early 2020 — including frequent hand-washing and staying home when they are sick.

There is no need for face masks in the United States, Messonnier said.

Yet at Mr. Ace, a hardware store in the Hoffman Estates neighborhood where the Chicago couple are hospitalized, sales of face masks have spiked over the past week.

“We can barely keep them on the shelves,” said owner Mike Patel. So far, the store has sold about 120 masks and has restocked them every three days.

“We keep getting them, and people are still buying them,” he said.

Mark Guarino in Chicago, James McAuley in Paris and Lori Aratani, Miriam Berger and Adam Taylor in Washington contributed to this report.