One person infected with coronavirus can result in hundreds of cases are called "superspreading events" which are not limited to mass gatherings. Understanding how Covid-19 has become highly infectious through certain individuals is essential to slowing down the pandemic as scientists are still developing a cure.
Dr. Anthony Fauci of the National Institute of Allergy and Infectious Diseases said that during the time President Donald Trump tested positive, at least 34 attendees at the Rose Garden ceremony tested positive as well. The superspreader event at the White House occurred when people were crowded together without wearing face masks.
Other superspreading events have occurred worldwide, including house parties, weddings, conferences, and factories such as meatpacking plants. There was even a case from South Korea where contact tracing isolated a single person as the cause of over 5,000 cases.
The Importance of Contact Tracing
In a recent study published in the journal Nature Medicine, researchers from the University of Hong Kong wrote about the results of contact tracing over 1,000 cases between January and April in the city.
They identified that 80% of the cases were local transmissions. By late August, there were over 4,000 confirmed coronavirus cases in Hong Kong since the first case in January.
The largest cluster they traced comprised 106 cases traced back to four bars in Hong Kong without the original source identified. In this cluster, the first cases were two customers in the same bar, who later infected two staff members just days later.
There were also several musicians from all four bars that tested positive for coronavirus. 73 of the cases were customers, staff, and performers infected at the bars while the remaining infections were family members, work colleagues, or friends.
Benjamin Cowling explained that a lot of positive cases around the world are not responsible for infecting others. Occasionally, some infect one or two, while others infect ten to twenty or more people.
How infectious the virus is dependent on the behavior of both people and Covid-19. Hong Kong's advanced contact tracing technology and efforts have determined that 80% of local transmissions were due to 19% of positive cases. On the other hand, nearly 80% of positive cases did not infect others.
Superspreading Events in Specific Environments
It was also determined that most superspreading events occurred indoors, such as bars, meatpacking plants, and prison. In another study, researchers analyzed how environmental conditions affect coronavirus droplets.
Using physics, aerodynamics, mathematical models, and relative humidity and temperature, droplet transmission was discovered to be highly dependent on the surrounding environment. A colder and humid climate allowed the droplets to travel as far as 12 feet after a person sneezes and the droplets evaporate much slower compared to a hot and drier climate.
William Ristenpart from UC Davis explained that "supertransmitter" might also produce a higher percentage of aerosols compared to respiratory droplets. "One possibility is that different individuals have respiratory fluid with different viscosity and interfacial tension, both of which affect the dynamics of droplet formation," he said.
It is important to focus on environments where superspreading occurs, especially indoor places, said Crystal Watson from the John Hopkins Center for Health Security. Many of these places, such as bars and gyms, have increased transmission because airflow has not been improved in such facilities. Many experts still recommend continuing basic health measures such as proper hygiene, wearing face masks, and physical distancing.
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