Coronavirus Latest: What Is A "Super-Spreader" And How Do They Shape An Outbreak?

Today the UK announced the identity of the British businessman who has potentially passed on the Wuhan Coronavirus to 11 people across three countries, qualifying him as a "super-spreader" of the illness. As the number of confirmed cases continues to rise globally, what do these super-spreaders tell us about the nature of pathogen spread, and how can we protect against it?

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Super-spreader is a term coined to describe an infected patient within an outbreak who passes on the infection to an above-average number of people. This varies depending on the illness, and it’s not the fault of the infected person. Some patients will infect many while some infect none at all and we have no exact method for identifying who is most likely to become a super-spreader. They have occurred in almost every major outbreak and have a significant impact on the movement and spread of disease.

Steve Walsh, a 53-year-old businessman from Brighton, England, first contracted the virus while attending a conference in Singapore at the end of January 2020. On his return from Singapore, he went on a skiing trip with friends to the French Alps before returning to London.

The average number of people infected by a single Wuhan Coronavirus patient has been reported to be between two to three people, but Walsh has been linked to four cases in the UK, five in France and one in Majorca, all of whom were in France with him. This level of spread is considered to be high enough above the average to qualify him as a super-spreader.

Walsh, who has now recovered but remains in quarantine at St Thomas' Hospital in London, issued a statement to the press, saying: "As soon as I knew I had been exposed to a confirmed case of coronavirus I contacted my GP, NHS 111 and Public Health England. I was advised to attend an isolated room at hospital, despite showing no symptoms and subsequently self-isolated at home as instructed. When the diagnosis was confirmed I was sent to an isolation unit in hospital, where I remain, and, as a precaution, my family was also asked to isolate themselves."

This pattern of spread has been seen historically in cases such as Middle East respiratory syndrome (Mers), another variety of coronavirus, which in 2015 saw 82 people infected from a single hospital patient. Speaking to the BBC, Nathalie MacDermott, from King's College London said of the Ebola epidemic in West Africa: “There were more than 100 new chains of transmission from just one funeral in June 2014”.

There are several factors that can contribute to someone becoming a super-spreader. Someone commuting daily on a busy train will come into contact with far more people than someone living and working in a rural area. Children are particularly good at becoming super-spreaders given their often-tactile nature, as well as those working in kitchens handling food. There are also some patients known as “super-shedders” who simply shed more of the virus or bacterial infection compared to others with the same illness, making them significantly more contagious.

Perhaps the most infamous example of a super-spreader was the case of Mary Mallon, better known to most as “Typhoid Mary”. Mallon was an Irish cook and the first known asymptomatic carrier of Typhoid fever in the US. Unaware that she was infected, she traveled around cooking for many families, sparking outbreaks of the disease across the country as she went. Eventually she was linked to the outbreaks and forced into confinement. She was later released under the agreement she would instead work as a laundress, but after realizing it didn’t pay as well she returned to cooking under a false name, causing further outbreaks and eventually leading to a second forced quarantine where she remained until she died.

The occurrence of super-spreaders highlights the need for continued vigilance with hygiene practices such as washing hands properly and the use of tissues. Super-spreaders cannot be expected to know that they are harboring an asymptomatic phase of disease, and therefore will be going about their daily lives as normal. In a government video released this week, China’s leader, Xi Jinping said, “Let’s not shake hands in this special time,” and I think we can all shake on that.

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