These people have been called “super-spreaders”, but do they really differ from the rest of us?
“It’s not a good concept to be labeled at the individual level,” says Dr. Jared Baeten, professor of public health and epidemiology and vice dean of the School of Public Health at the University of Washington. “But I think it helps people think about how a virus like this can get through communities quickly.”
It may be that a so-called super-spreader is the right person in the wrong place at the wrong time.
“Some individuals are either particularly contagious or that [amount of] time or the number of people they spend time is enough to affect the spread of the virus so that it is disproportionately larger than average, “Baeten said.
Measure how viruses spread
First a little science. Infectious disease specialists and epidemiologists, have a number to describe how infectious a disease is. It is called the reproduction number or R-nothing, written R0. It is basically a measurement of the average number of people that an infected person continues to infect.
“How contagious a disease is, you classify it by this R-zero factor. The R-zero factor is somewhere between 2 and 3 for coronavirus. For measles, it’s much higher – it’s between 16 and 32,” Dr. Rob Murphy, Professor of Infectious Diseases and Biomedical Engineering and Executive Director of the Institute of Global Health at Northwestern University Feinberg School of Medicine.
A disease’s reproduction number can change as time goes on; it can also be different in different places. The goal is to get it as low as possible.
“All you have to do to get rid of an epidemic is that the R node factor is less than one. As soon as it’s less than one – each person gives it to less than another person – it dies off,” Sa Murphy . “The problem with the R-nicked factor is that it is very nice to describe the mean. But in medicine, as in many things, if you find an average person let me know; I want to go and meet them.”
In other words, experts believe that most people infected with the virus are so-called “dead ends,” which on average infect fewer than one, and a small percentage of people infected with the corona virus that cause Covid-19 infect many more people than average.
What makes super-spreading possible?
One reason why someone can infect more people than others comes to individual bodies.
“Everyone is different, they handle the virus in their bodies differently,” Murphy said. “So some individuals, they have what we call a high viral load – it’s just the amount of virus per drop. Some people have 10 or 100 times more virus in their drops than other people.”
Baeten agrees. “There are things that we don’t quite understand about this virus, but usually with viral infections there are a number of viral loads and some people – either because of how the virus interacts with their immune system or their genetics – have a higher viral load than others. And higher viral load probably means that they are more contagious to people they come around. “He adds that the length of the contacts is also very important.
Both Murphy and Baeten say that behavioral aspects can also play a role.
Does anyone speak out loud? People who speak loudly (or sing or squeal during exercise) are believed to release more virus-laden drops into the air because of what they do or how they do it.
Is that person an extrovert who likes the company of others or the hug-fine kind that comes physically close to others? Now we have all been educated on the benefits of isolating and social distance to keep the infection level down – but even during a pandemic this does not always happen.
Another factor that can lead to super-proliferation is timing. Studies have found that people start dropping virus particles about two days before they start showing symptoms, when they are pre-symptomatic; others never experience symptoms of Covid-19 at all – asymptomatic – but still lose the virus. People in both of these groups circulate throughout the day unconsciously infecting others.
“The unfortunate thing about transmitting disease is right when the infection is gaining momentum, just before a person becomes symptomatic, they probably have the highest level [of virus]”so Murphy.” So the day they start having symptoms, and the day before and maybe the day before that is when they have the highest viral load. “
Location, location, location
Also important is the opportunity to spread. “Just because someone has a high viral load doesn’t make them a super spreader if they’re behind a mask [or] at home, “said Baeten.” Because the super-spread happens when someone who can transmit the virus is in contact with enough people that they end up spreading the virus to more people than the average. ”
This is where places – such as a crowded nightclub, a worship service or a meat packing facility – come into play. “These are all kinds of events that can be a setting to have a large spread,” Baeten says. “Introduce someone who is contagious – and maybe not even super-infectious – to a number of people up close for a long time – as a funeral, as a sports event, as a nursing home – and that can enhance the spread.”
Epidemiologists have a way of catching the type of disease that clusters across sites – it’s called the spreading factor (or “K”).
“In a way, it’s a measure to give you a sense of, is this a disease that occurs randomly over time and place, or is it a group that is clustered in time and place,” explains Michael Osterholm, director of the Center for Infectious Disease Research and politics at the University of Minnesota. “If you have 100 cases, they will be distributed randomly, like every foot apart … Or you can have the same 100 cases in the same space but merged, so a group here [of] 30 people very close to each other, another over there. So it’s an attempt to measure is how random [or clustered] they occur in that space. “
Another way of thinking is that the spreading factor measures how many cases of infection are responsible for all transmissions. The lower the number, the more “clusters” the disease around super-spreading events or places.
“We know that the transmission of many infectious diseases is heterogeneous – different people transmit more and different settings are more favorable for transmission than others (eg indoors more than outdoors). This seems especially so for this new coronavirus with the spread factor analysis which indicates that 10% of the cases cause 80% of infections, “she wrote in an email.
As for where these clusters have occurred, “In our database of settings linked to transfer, we found the usual suspects (healthcare and cruise ships, etc.) but some odd things, such as more meat processing facilities, and fewer schools than we’d expect . “She adds to the list of” large, shared accommodations “that work dormitories and refugee camps.
“We haven’t found any protests that are still associated, but we’re really looking at settings rather than events,” says Knight. “I can imagine that protests may not be as risky as they are outdoors, but then the individuals may be involved in screams (which can be risky for transmission) and they may be in close contact for a long time.”
Put the pieces together
Knowing that transmissions of coronaviruses often occur in clusters linked to certain settings and through certain individuals can help inform how governments, public health experts and society try to control it.
Murphy adds that “massive testing – five times more than we have” is also needed to confirm who is sick with Covid-19 and to identify who can be infected and walk around without symptoms. “You have to identify them,” he said. “So basically test everyone and then quarantine the people who are infectious. That would make it alone.”
But he points out that barriers to testing (such as cost and availability) must be eliminated or “people will just let go of the system.” He foresees a time not so far in the future where people can be tested and get their results in place, or even test themselves at home.
Moving focus from individuals’ actions to locations, says Knight, “We may need to tailor exit strategies from lockdown to target certain locations more than others – for example, risky settings should be kept closed or visits to these settings should be monitored in contact tracking Apps. By understanding where and from whom the transfer occurs, we can intervene to stop it. ”
He argues for a more targeted strategy.
“Understanding that the entire thesis on contact tracking can only fall on this particular issue [of super spreaders], “he says.” If you have a small number of cases, you can clearly try to contact tracking of all of them, and you do not wonder if they are super-spreaders or not. With many thousands of cases, you will always try to determine: what is the highest priority? If you do not know who the super-spreaders are, there is no way you can [factor] “But therein lies the rub,” he says: “Contact tracking will not identify these people until long after they are ill. “And then the damage will have been done.
No one knows who is super-spreading – not even the one spreading the virus – until it’s too late
“If we could identify super-spreaders early, it would help, but at this point we have no reasonable way to do that,” Osterholm said. “There’s no big double S on their forehead that says ‘Super Spreader’ so we can find them. And that’s the challenge.”
Murphy has a slightly different take. “If they are super spreaders or just regular spreaders, then it makes no difference – they spread,” he said.
In the end, Baeten said, it will all of us, because we’re in this together.
“I think it is up to all of us to do our best not to be a super-distributor by staying away from large crowds and major attractions where we might be able to spread the virus and by wearing a mask.”