One more instance of a superspreader spreading coronavirus to 71 people in China has been documented. The superspreader continued to remain asymptomatic for over a month after arriving in China and spreading the virus.

Many instances of a single person spreading novel coronavirus to dozens of people have already been documented. People who spread the virus to many are often referred to as superspreaders.

According to the MIT Technology Review, in the case of novel coronavirus, the precise number of people who should be infected by a single person t be called as a superspreader hasn’t been defined yet. “But generally speaking it far exceeds the two to three individuals researchers initially estimated the average infected patient could infect,” it says.

The biological reason why certain people turn out to become superspreaders is not known. “It might have something to do with increased viral loads and shedding more virus than is normal,” the MIT Technology Review says.

Known superspreaders

For instance, a single person in a choir practice in Washington State infected about 52 people, while a person who had returned from the U.S. led to massive spread of the virus in South Korea. The transmission in South Korea happened to people belonging to the Shincheonji Church sect members. “About 60% of the country’s more than 4,000 confirmed cases are sect members,” says a BBC report. The third well known instance was in a wedding ceremony on March 13 when the bride’s father, who had arrived from Spain, had apparently spread the virus to 76 people.

Now, an asymptomatic traveller who arrived from the U.S. to Heilongjiang Province in China on March 19 had apparently spread the virus to 71 people by April 22, a study published in Emerging Infectious Diseases says. The first case in this cluster was confirmed on April 9.

“Our results illustrate how a single asymptomatic SARS-CoV-2 infection could result in widespread community transmission. Continued measures to protect, screen, and isolate infected persons are essential to mitigating and containing the COVID-19 pandemic,” they write.

The first person to be infected by the index cases lived in the same building and the researchers believe that the contact was infected via surfaces in the elevator in the building where they both lived.

On April 15, the Chinese Center for Disease Control and Prevention sequenced the entire genomes of 21 samples from the cluster. “Viral genomes were identical in 18 cases and 3 other cases had a difference of 1–2 nucleotides, indicating that SARS-CoV-2 came from the same point of origin,” they write. As the genome sequence was very different from the ones circulating in China, the researchers concluded that the virus had a foreign origin and was brought to the Province by a traveller. Genome sequencing helped identify the index case.

Asymptomatic transmitters

The Heilongjiang Province superspreader who had arrived in China on March 19 remained asymptomatic as late as April 22, even while spreading the virus to 71 people. This is the first instance when a superspreader has been known to be asymptomatic.