SEOUL, March 26 (Yonhap) -- Extensive testing and tracking people who have come into contact with coronavirus patients prevented a once-alarming cluster in South Korea from spiraling out of control, an investigation showed Thursday, offering implications for how other nations build the first line of defense against the virus pandemic.
Alarms were raised on March 8, when an employee at an insurance company's call center in Seoul's bustling Guro district tested positive for the virus, according to the epidemiological investigation into the cluster outbreak, conducted by the Korea Centers for Disease Control and Prevention (KCDC).
At that time, health officials warned that the call center could become the worst coronavirus cluster in the Seoul metropolitan area, home to about half of South Korea's 51 million population.
Hundreds of employees had worked in confined rooms without wearing masks at the call center. There were restaurants, coffee shops and convenience stores inside the 18-story building that houses the call center.
Although most of some 550 co-workers at the call center live in Seoul, others live in neighboring areas, including Incheon and Gyeonggi Province.
Over the next three days, the building was shut down, and makeshift testing facilities were set up in front of the building.
A total of 1,143 people who were linked to the building got tested by March 12, the investigation showed.
Among those who got tested were people who worked or lived at the building between Feb. 21 and March 8, a two-week period they might have come into contact with the first known patient at the call center.
Mobile-phone messages were sent to a total of 16,628 people who visited the building during the two-week period, advising them to get tested if they show symptoms.
On March 11, or three days after the first patient was identified, Seoul Mayor Park Won-soon said 93 people who were linked to the call center, mostly call center co-workers and their family members, tested positive for the virus.
For those who tested negative, they were required to self-isolate at home for two weeks and install a smartphone app that allowed them to be put under supervision if they showed symptoms.
So far, 160 people who were linked to the call center -- 97 co-workers and their 63 family members or friends -- have tested positive for the virus.
The investigation concluded that, "Early identification of the first patient and containment measures helped stop a further spread" of the novel coronavirus.
The investigation also noted the high risk of the infection spreading in confined spaces, such as call centers, hospitals, homes and churches, as the coronavirus is transmitted through respiratory droplets.
The first patient worked on the 11th floor of the building. Of the 214 co-workers on the 11th floor, 94 people, or 43.5 percent, tested positive.
However, only two of 27 co-workers who worked on the 10th floor tested positive. For the ninth floor, where 206 co-workers worked, only one person tested positive, according to the investigation. No infection has been confirmed on other floors of the building so far.
Of 226 family members of the 97 co-workers who tested positive, 34 people, or 15 percent of all infections linked to the call center, have tested positive for the virus.
The investigation found a "significant scale of infection on the 11th floor," while suggesting that, "The possibility of spreading infection through a brief in-person meeting is extremely low."
Health authorities also confirmed that "the possibility is low" for the virus to spread through a "brief and ordinary contact," such as touching surfaces like elevator buttons or door handles at the infected area.
After analyzing ventilating systems of the building, the investigation found no evidence that the virus can spread through the ventilating systems.
Citing the cluster outbreak at the call center on the 11th floor, where people were infected with the virus after sharing confined spaces for long hours, the investigation urged health authorities to take extra precautions when a virus patient is confirmed at "high-risk" facilities, such as call centers, hospitals, homes and churches.
South Korea began implementing stricter rules on social distancing Sunday to slow the coronavirus pandemic that emerged in China late last year.
Citizens are strongly urged to stay at home, except for essential needs or jobs, with the government restricting religious gatherings, indoor sports activities, and visits to nightclubs and other entertainment venues.
South Korea's coronavirus caseload stood at 9,241 on Thursday, with the virus claiming 131 lives.
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