Barely more than a week ago, South Korea's coronavirus outbreak appeared to be contained as the number of confirmed infections stabilized at 30. Sensing a turning tide, many Seoul residents took off their surgical masks and resumed riding the subways and shopping at malls.
Then, on February 17, a 31st case surfaced at a health clinic in Daegu, a city about 241km south of the capital where the vast majority of known infections were located. An unidentified 61-year-old woman, who lived there and occasionally commuted to Seoul, tested positive for the novel coronavirus.
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It seemed like a standard case until public health authorities started tracing the patient's tracks. What they learned shocked them: the woman had, during the previous 10 days, attended two worship services with at least 1,000 other members of her secretive religious sect whose leader says the end of days is coming.
Within 24 hours, the nation's number of confirmed cases started multiplying exponentially. The tally rose by 20 during that period, doubled the following day and then doubled again on the third day.
By Wednesday, the count skyrocketed past 1,000 - a more than 30-fold increase in a week that prompted the government to raise its health alert to the highest level. At least half of the new cases are linked to the sect called the Shincheonji - which translates to "new heaven and land" and whose members worship side-by-side in cramped spaces.
"What made this case so much worse was that this person spent a considerable amount of time in a very crowded area," said Kim Chang-yup, a professor for health policy at Seoul National University. "There's growing fear and resentment among the people right now."
South Korea's health ministry said Wednesday it was launching a manhunt for more than 212,000 members whose names were provided by the sect. Korea's Centers for Disease Control & Prevention already is screening 9,300 sect members, in addition to those who attended the two services. On Wednesday, it expects to conclude tests of 1,300 sect members showing symptoms.
212,000people, whose names have been provided by the sect, are being tracked down by the health ministry.
Yoo Il-han, a former member who runs a counseling center for those wanting to leave the group, said health officials will have a difficult time tracking people down. The sect is protective of its members and warns that Satan will use their families to try to influence them.
"Concealment is the key," he said. "They tell you: Don't tell anyone, including your family members, what you believe in, and don't believe what you see about Shincheonji online."
Patient 31 first checked into the Saeronan Chinese Medicine Hospital on Feb. 7, complaining of headaches after being involved in a car accident the day before. According to the hospital, the patient didn't have any record of travelling overseas nor any known contact with a coronavirus patient. She also didn't have any fever, cough or respiratory symptoms.
On the third day of being hospitalised, the patient developed a fever and received a flu test, which came back negative, according to the hospital.
The next day, she left the hospital for two hours to attend a morning service at the Shincheonji church in southern Daegu, according to Korea's CDC. It's common in South Korea for hospital patients to come and go - even walking outside wearing hospital garb and wheeling intravenous drips alongside them.
The woman also had lunch with a friend at a hotel in eastern Daegu on Feb. 15 and attended another Shincheonji worship service on Feb. 16, the country's health authorities said.
It wasn't until Feb. 17, as her condition worsened and a scan showed signs of pneumonia, that doctors were prompted to test for the coronavirus. Ten days after Patient 31 first set foot in a hospital, her infection was confirmed after a diagnosis at a public health clinic.
Health officials in South Korea still don't know how she was infected, and how she spread the virus to fellow Shincheonji members.
The religious movement was founded in 1984 by Lee Man-hee, now 88.
The group's emphasis on continually gathering for worship, recruitment and other activities may be the root cause of the cascading number of infections among Lee's disciples, said Stella Kang, a former sect member.
Their belief system is that the end time is coming soon and our physical body is not as important. So even if you are really sick, you have to go to the church because that gives you the word of life."
At the two worship services attended by patient 31, more than 1,000 people sat on the floor, elbow-to-elbow and knee-to-knee, for as long as two hours.
"Their belief system is that the end time is coming soon and our physical body is not as important," Kang said. "So even if you are really sick, you have to go to the church because that gives you the word of life."
The group's website previously said it opened a church last year in Wuhan, the epicenter of the virus outbreak, though that detail subsequently was removed. The sect later said on its website that it switched all services in Wuhan online in 2018.
Separately, authorities are trying to determine whether patient 31 is connected to an outbreak at another hospital outside Daegu, where a funeral for the brother of the sect's leader was held earlier this month.
In South Korea, funerals often are carried out at a facility adjacent to a hospital, and attendees eat and drink together in a nearby room. Many funeral homes, which resemble conference centers, have multiple services taking place simultaneously within their complexes.
Alarmed by a sudden surge in infections not seen since the swine flu epidemic that killed 250 people in South Korea in 2009, the government elevated the national health alert to its highest level.
Schools postponed reopening, the military banned leaves and visits, and companies began canceling events and implementing work-at-home policies. More than a dozen countries subsequently banned or restricted the entry of South Korean nationals.