The man arrived at the hospital with a fever and a bad cough. Relatives accompanied him through the doors, beneath the red neon sign reading "Emergency."

It looked like pneumonia, but when doctors at Community Hospital learned that the patient was a healthcare worker in Saudi Arabia, they began suspecting something more sinister.

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FOR THE RECORD

MERS virus: An article in the May 10 Section A said a man infected with the deadly Middle East respiratory syndrome, or MERS, took a bus trip from Chicago to Indiana on April 27. He made the trip on April 24, the same day he arrived in Chicago on a flight from Saudi Arabia. —

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Swabs from the man's nose and mouth confirmed it: The United States had its first case of a new and often deadly ailment called MERS, or Middle East Respiratory Syndrome, and health experts were facing a medical drama that all of them had anticipated but none of them ever hoped to see.

Over the last week, investigators have worked to track down every person who shared space with the unidentified elderly patient before he showed up at the hospital, including passengers on the April 24 flight that brought him from the Saudi capital of Riyadh to Chicago O'Hare International Airport. Through passenger manifests, credit card receipts and other clues, they have also traced people who rode with the man on the bus he took from the airport to northwestern Indiana on April 27.

So far, nearly all the fellow travelers — about 112 — have been traced, and none has tested positive for the crown-shaped virus that causes MERS. At least 50 hospital workers who had even the slightest contact with the man remain in home isolation, but they also show no symptoms. The same is true for the Indiana relatives whom the man, an American living in Riyadh, had come to visit.

On Friday, the MERS patient was cleared to leave the hospital and authorized to travel.

"It appears we have contained this," Alan Kumar, chief medical information officer at Community Hospital, said this week.

For the last two years, since the virus that kills one-third of those it infects first appeared on the other side of the world, on the Arabian Peninsula, U.S. epidemiologists have waited and prepared for the day it would appear in this country.

"Anyone is a planeload away from any disease on Earth," said Indiana's state epidemiologist, Pam Pontones.

The response in Munster, a bedroom community about 30 miles south of downtown Chicago, was a textbook example of how the public health system is supposed to work, said those involved in this case, citing the rapid diagnosis and the quick tracing of the patient's contacts.

Warnings from the federal Centers for Disease Control and Prevention were carried to state health officials and from there to healthcare workers on the front lines — who, months down the road, remained attentive enough to ferret out an infected patient in time.

"It's really cool, when you think about it," said Johns Hopkins epidemiologist Trish Perl, who studies the virus.

But medical experts say that although this case was handled successfully, it is a sign of things to come and highlights the need for continued heightened vigilance, as people crisscross the globe with greater frequency than ever before.

"It's a small world these days," said Daniel Feikin, an epidemiologist with the CDC in Atlanta. Feikin was the leader of a six-member team of specialists who came to Indiana on May 2, the day the agency confirmed the Munster patient had MERS.

"Diseases don't respect borders," Feikin said. "In this day and age, we need to be prepared for diseases coming to the United States."

Health officials have been keeping a close eye on the virus since scientists first discovered it in a 60-year-old Saudi man, who died in 2012 after suffering pneumonia and kidney failure. By June 2013, nearly 80 people in the region had been infected with MERS, and more than half had died. Saudi Arabia, which has been hit hardest by MERS, reported Wednesday that it had recorded 449 cases and that 121 of those infected had died.