Why some viruses have ‘super-spreaders’
Sarah Newey analysis
Experts are increasingly concerned that “super-spreaders” could make the coronavirus outbreak difficult to control and its trajectory harder to predict.
The term describes an individual who infects a disproportionately high number of people.
It is known to occur in some viruses but not others — and scientists do not know why.
Some diseases, such as flu, have relatively stable transmission rates; every infected person would be expected to pass the disease on to one or two others. In the case of the new coronavirus, known as 2019-nCoV, it appears some individuals will not infect anyone, while others could pass the disease to tens of people.
“Not all cases are equal, but we don’t know much about the biological basis behind this,” Mark Woolhouse, professor of infectious disease epidemiology at the University of Edinburgh, said.
“It seems to be largely to do with the way an infection proceeds in a specific individual, which means some people simply excrete more virus than others,” he said.
“So they’re more infectious and become super-spreaders.”
Environmental factors, such as close contact in hospitals, poor infection control mechanisms and lackadaisical hygiene, can also increase the chance of superpreading.
The potential becomes greater if super spreaders pass on the infection before they have shown symptoms, as is the case with 2019-nCoV.
This form of transmission appears to be taking place in the current outbreak. which has now infected close to 38,000 people.
Unpredictable transmission is a characteristic of several infectious diseases. In 2015, a patient in South Korea with Middle East respiratory syndrome infected 82 others — half of all the cases in the country — in an overcrowded hospital.
Mysteries remain about what exactly turns an individual into a super-spreader, and this form of transmission makes containment of an outbreak far more challenging.
“This has big implications for how we try to tackle the coronavirus,” said Professor Woolhouse.
“It means we have to be even more vigilant so we detect and isolate cases early . . . If you miss even one case, and that person turns out to be a super-spreader, then there’s the potential to spark off another train of transmission.”