Eight days after returning from a trip to the Middle East, a 68-year-old South Korean man developed a cough and fever.
He visited four health facilities seeking treatment and inadvertently triggered the biggest outbreak of Middle East Respiratory Syndrome (MERS) outside that region, and what is verging on national panic at home.
President Park Geun-hye has said everything must be done to stop the outbreak that has infected 34 other people as of Thursday, and killed two of them in South Korea.
Hundreds of schools have locked their gates as the outbreak rekindled fears of a similar coronavirus that caused Severe Acute Respiratory Syndrome in 2002, and killed about 800 people as it spread around the world.
The South Korean "index patient" was running a farm equipment company in Bahrain, according to a South Korean official, and had visited the region before returning on May 4.
More than half of South Korea's infections have been traced to a hospital in Pyeongtaek city, 65 km (40 miles) southwest of Seoul, where the man shared a room with another patient.
"The first patient was close to another person in the room and it appears that more infections took place as he went out of the room for checks, sneezing and coughing in the hall," said Kim Woo-joo, an infectious disease specialist advising the government.
Others became infected at three of the four health facilities the man visited, authorities said.
Officials have not identified the hospitals where MERS patients are being treated, but the Pyeongtaek facility has been shut and staff quarantined.
A nurse there said there was a lack of knowledge about the virus when the man was hospitalized. Health officials have said hospital staff had not been aware of the man's Middle East trip.
"There's little understanding. His visit to us was just unavoidable exposure to other people in the hospital," the nurse, who is in quarantine at home, said by telephone. She declined to be identified.
When the man was admitted at another hospital, where he was finally diagnosed, he at first only told staff he had visited Bahrain, which is not considered a MERS danger zone, health officials said.
In fact, the man had also been to Saudi Arabia and the United Arab Emirates, the countries with the most MERS cases and most of its approximately 440 fatalities.
"We reported him to the disease control center but because he went to Bahrain, which was all we knew at that time, his case dragged on," said an official at the hospital where he was diagnosed on May 20, who also declined to be identified.
"Too much time was spent finding him positive."
The person the index patient shared a room with at the Pyeongtaek hospital contracted MERS, as did that person's son, who had visited.
The son broke voluntary quarantine and traveled to Hong Kong and mainland China, where he was diagnosed with MERS. He is in hospital in China.
As of Wednesday, the index patient was on a respirator in a government-designated hospital. His 63-year-old wife also contracted the virus, but authorities said her condition had improved.
Authorities believe that other than the index patient, most of the MERS infections in South Korea came from the health facilities the index patient visited.