Coronavirus: super spreaders could disrupt efforts to contain outbreak, say expertsMegan Orito
Coronavirus: super spreaders could disrupt efforts to contain outbreak, say experts.
A passenger wearing a mask and covered with a plastic bag walks outside the Shanghai railway station CREDIT: ALY SONG/REUTERS
Experts are increasingly concerned that “super spreaders” could make the coronavirus outbreak difficult to control and its trajectory harder to predict.
The term is used to describe 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 onto one or two others.
In the case of the new coronavirus, currently known as 2019-nCoV, it appears that some individuals will not infect anyone, while others could pass the disease to tens of people.
While the phenomenon has long been observed, little is understood about why it happens.
“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, told The Telegraph.
“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 – including close contact in hospitals, poor infection control mechanisms and lackadaisical hygiene – can also increase the chance of super spreading events.
This potential becomes even greater if super spreaders can pass on the infection before they have shown symptoms – throughout the current outbreak there have been concerns that people can transmit the coronavirus before they fall ill.
This form of unpredictable transmission appears to be taking place in the current epidemic, which has now infected close to 38,000 people.
A British man who attended a conference in Singapore and a ski resort in France before flying home to Brighton passed the virus onto at least five others, while a study in JAMA journal has described how one patient infected at least 10 health care workers in Wuhan hospital.
But the phenomenon, though worrying, is not unexpected. Unpredictable transmission is a characteristic of several infectious diseases, including Ebola and tuberculosis, and has been observed during previous coronavirus epidemics.
The international spread of Sars (severe acute respiratory syndrome) in 2003 was fuelled by a Chinese doctor who travelled from the epicentre of the outbreak to Hong Kong, where he infected fellow hotel guests who subsequently took the disease home to five other countries.
Similarly in 2015, a patient in South Korea with Mers (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, but there is a consensus that this form of transmission makes containment an outbreak far more challenging.
“This has big implications for how we try to tackle the coronavirus,” said Prof Woolhouse. “It means we have to be even more vigilant so we detect and isolate cases early – that’s currently the only way to contain and spread the virus.
“The case of the traveller from Singapore is just an illustration of what happens if you don’t,” he added. “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.”
Jonathan Ball, professor of virology at the University of Nottingham, added:
“We often think of super spreaders as producing lots of virus, which translates to a lot of transmission potential and suggests they are showing symptoms. But it sounds like this guy was not super ill in France, so it’s going to be important moving forward to know if he had overt symptoms or not.”
But Prof Ball said that at this stage we also don’t know how much of a contribution individual super spreaders have to the transmission of the new coronavirus.
“Of course super spreaders can exacerbate the outbreak. [But] we need to understand transmission dynamics to see much how different individuals with different symptoms are contributing to the disease.”