A study recently published in the journal Emerging Infectious Diseases illustrates the progression of the COVID-19 coronavirus outbreak on the 11th floor of a high-rise building, which saw a virus attack rate of 43.5%, with most of the confirmed cases working on one side of the building.
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South Korean study on COVID-19 transmission in high-rise office
When South Korea's COVID-19 outbreak happened in February, the country's coronavirus tally jumped from a few hundred to more than 6,000 in weeks, which is when health authorities took aggressive action, reports Business Insider. In a flash, they implemented widespread testing and contact tracing, then employed text-messaging and apps to alert people about potential exposures and help ensure that people in quarantine stayed home.
In March, 97 of 811 employees at a Seoul call center tested positive for the novel virus, according to the study from Korea Centers for Disease Control and Prevention (KCDC) — South Korea's national public health authority. Of these, 94 sat on the same floor (the 11th) — with 79 workers in the same section, according to the KCDC study.
The rate of secondary (repeat) coronavirus attacks among case-patients previously found to show symptoms was 16.2%. Merely 4 case-patients who tested positive without symptoms remained asymptomatic throughout their 14-day quarantine, and none of this group's household contacts contracted secondary infections, according to the study.
Additionally, a color-coded seating chart created by the KCDC shows the distribution of the call-center employees across the 11th floor. Blue desks are the work stations of those who contracted the virus.
Close quarters were key to South Korean COVID-19 outbreak
The chart above reveals how close-quarters workers' experience — compounded by long periods of remaining in mutual vicinity — easily allows the COVID-19 coronavirus to spread.
"Despite considerable interaction between workers on different floors of building X in the elevators and lobby, spread of COVID-19 was limited almost exclusively to the 11th floor, which indicates that the duration of interaction (or contact) was likely the main facilitator for further spreading," wrote the KCDC in its report.
On March 8, the Seoul Metropolitan Government was told of one (unnamed) employee working at the Seoul call center in building X, who tested positive for coronavirus infection. They worked on the 10th floor, and never visited the 11th, reports the KCDC.
Locking down a skyscraper of residents and workers
What happened after was already standard procedure in South Korea: The skyscraper that housed the call center's offices was closed the next day, and all who lived or worked in the building self-quarantined for two weeks. The high-rise features both commercial and real estate on its first 11 floors, with residential apartments on from the 13th to the 18th floors — which meant not just workers, but also residents made regular contact in the lobby and elevators.
This is when a team of federal employees came and tested all residents and workers — in addition to others present in each resident's household. Any people testing negative were re-tested within the two-week quarantine period. Together, 1,143 people who often visited the premises were tested.
"This outbreak shows alarmingly that severe acute respiratory syndrome coronavirus (SARS-CoV-2) can be exceptionally contagious in crowded office setting such as a call center," read the KCDC study. "The magnitude of the outbreak illustrates how a high-density work environment can become a high-risk site for the spread of COVID-19 and potentially a source of further transmission."
The South Korean federal team sent text messages to anyone who persisted in the vicinity of the building for more than five minutes — amounting to more than 16,000 — to warn people of potential exposure and advise immediate testing.
"By testing all potentially exposed persons and their contacts to facilitate the isolation of symptomatic and asymptomatic COVID-19 case-patients, we might have helped interrupt transmission chains," wrote the KCDC in the report. "In light of the shift to a global pandemic, we recommend that public-health authorities conduct active surveillance and epidemiologic investigation in this rapidly evolving landscape of COVID-19."
Limitations of coronavirus outbreak study
However, the outbreak investigation had numerous limitations, according to the KCDC. They were unable to track the cases from building X to other clusters of coronavirus infection, which makes it hard to know exactly what role each case-patient made in the larger-scale wave of infections that swept through the country.
Additionally, the KCDC didn't have direct access to clinical information all of the confirmed cases, which prohibited the study from giving a detailed description of clinical syndromes. But the study succeeded in showing the power of screening every potentially exposed person, and show how containment can work as planned in the middle of a nationwide COVID-19 outbreak.
"By testing all potentially exposed persons and their contacts to facilitate the isolation of symptomatic and asymptomatic COVID-19 case-patients, we might have helped interrupt transmission chains," read the KCDC report. In view of the larger stage of the global coronavirus pandemic, the KCDC recommends public health authorities exercise "active surveillance and epidemiologic investigation in this rapidly evolving landscape of COVID-19."
This study plainly shows the serious threat coronavirus outbreaks pose among people enclosed in office workplaces. While many office-goers are working-from-home, the KCDC says preventative strategies may be best to lower the risk of employee infection, if and when they return to office-based work.