Superspreaders Are a Covid-19 Mystery

Like Typhoid Mary, some people are experts at passing along infection. No one knows why.

The Covid-19 pandemic has brought with it an evocative term: superspreader, a person who spreads infectious disease to an unusually large number of others. Superspreaders have had a role in numerous epidemics and outbreaks in modern history.

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Mary Mallon, seen here, was known as Typhoid Mary. (Getty Images)

One notorious superspreader was Mary Mallon. Mallon worked as a cook in New York in the early 1900s and for much of her life was an asymptomatic carrier of the typhoid bacteria. Known as Typhoid Mary, she infected more than 50 people and was sent to live in quarantine for over 25 years.

During the SARS epidemic of 2003, roughly half of the more than 8,000 cases recorded were traced to a single individual who had spent one night at a Hong Kong hotel. He infected more than a dozen hotel guests, who in turn spread the disease to Canada, Singapore, and Vietnam. During the smaller outbreak of MERS in South Korea in 2015, over 80 percent of all cases were traced to five individuals. One person alone was responsible for infecting 84 others. The spread largely occurred inside hospitals.

In recent months, there have been reports of religious services, parties, funerals and conferences that resulted in clusters of infections. But it’s not yet clear how significant superspreaders have been to the spread of Covid-19.

This article was adapted from a Twitter thread created with support from a Brown Institute for Media Innovation grant recognizing the need for accurate information about the Covid-19 virus. Learn something new from history: Subscribe to our newsletter, and follow us on Twitter @RetroReport.