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Updated: Mar 22, 2020 20:11 IST

Highlights A super-spreader spreads infection among large number of people

During the Covid-19 outbreak in India, doctors and researchers will also come across super-spreaders

A woman in South Korea infected 37 people in her church during the current outbreak

A Super-spreader may sound like someone who is generous in spreading around energy or love, but for experts in infectious disease, the term means entirely something else and has no positive connotations. A super-spreader is the one person who is responsible for spreading infection among an unusually large number of people. Mary Mallon, known to the world as Typhoid Mary, was a super-spreader of the disease.

Mallon was an asymptomatic carrier of typhoid and is thought to have infected how many people, how many some of whom died of the infection. She worked as a cook for affluent families in New York. In 1907, a medical researcher identified her as someone who may have infected many and caused outbreaks of typhoid. Mallon was forced into quarantine on different occasions for a total of 26 years until she died in 1938.

During the Covid-19 outbreak in India, doctors and researchers will also come across super-spreaders.

In an Elsevier piece in 2010, Richard A Stein, a scientist from the Department of Molecular Biology, Princeton University, wrote that identifying super-spreaders can give doctors important clues on managing an infectious disease. He cited several examples. In 1960, researchers described some infants as cloud babies who, after catching a respiratory virus, became highly contagious and were able to spread Staphylococcus aureus (a bacterial infection) widely in the nursery. In early 1983, a nurse infected with the same bacteria was linked to staphylococcal skin infection outbreaks in two nurseries from two different Florida hospitals. Super-spreaders were identified during the Severe Acute Respiratory Syndrome (Sars) outbreak, too.

But a super-spreader gains that distinction based on a combination of factors: immune suppression, delayed diagnosis and quarantine, and misdiagnosis, among many others. For example, a Kalyan resident who has tested positive after returning from the US, is believed to have come in contact with more than 1,000 people. He travelled by train to where and when attend a wedding. A 46-year-old man from Delhi came in contact with 813 people from the time he returned from Italy on which day to testing positive for Covid-19 about 20 days later. The man travelled by metro to work and came in contact with a number of people at work.

“”The term super-spreader is not described in medical science. But this is basically a person who is capable of infecting several persons. The person may be asymptomatic and hence not in quarantine. The person may not have practised social distancing and may have hugged or shook hands with non-infected persons. We have also seen that those with low immunity transfer more infection. It’s called inoculation,” said Dr BK Tripathi, professor of medicine at Safdarjung Hospital.

A woman in South Korea infected 37 people in her church during the current outbreak, according to news reports . There is also research on super-spreader events; the outbreak of Covid-19 in Wuhan coincided with the Spring Festival in China when there is a lot of public movement in Chinese cities.