Ask an Infectious Disease Expert: What Is a Superspreader?

Makeda Robinson, MD, PhD, is an infectious disease specialist currently studying virus-host interactions in emerging viruses at Stanford University. Each week, Dr. Robinson breaks down complicated COVID-19 topics and addresses pressing public health concerns.

From family weddings to campaign rallies, gatherings of all kinds during the COVID-19 pandemic have the potential to become "superspreader events." And as the weather cools and people begin to spend more time inside, we'll probably be hearing about superspreaders even more.

What makes a person a superspreader? Is it their basic biology, the amount of virus in their system, or just bad timing? And which elements combine to create a superspreader event? Dr. Robinson explains how to understand, prevent, and respond to superspreader events.

Verywell Health: What is a superspreader?

Dr. Robinson: A superspreader is a person infected with the SARS-CoV-2 virus who is able to transmit the virus to a disproportionately high number of people. 

Verywell Health: To what degree are superspreaders responsible for coronavirus transmission? 

Dr. Robinson: A study that came out of India showed that as few as 5% of infected carriers are responsible for up to 80% of the secondary infections. This is one of the largest transmission studies for COVID-19 to date, which included almost 85,000 infected individuals and traced infection rates in 575,071 exposed people. However, the concept of superspreaders is not unique to COVID-19. Other related viruses, including SARS-CoV, MERS, and Ebola, have also been shown to have the potential to spread in this manner; SARS-CoV-2 just seems to be much better at it. 

Verywell Health: What factors exacerbate superspreader events? 

Dr. Robinson: There are three major ingredients to think about in the setting of a superspreader event, or SSE: The host (us), the pathogen (SARS-CoV-2), and the environment (number of other people, ventilation, social distancing, mask usage, etc.). All of these factors play a role in the development of a SSE, and altering one aspect can prevent and exacerbate the outcomes.

SSEs tend to occur when the infected individual has a very high viral load. While poorly ventilated and indoor spaces can also exacerbate SSEs, it’s important to remember that SARS-CoV-2 can also spread through small airborne particles or “droplet nuclei,” which can be spread outdoors by the wind. You may not have to be sitting directly next to the infected person to be affected. 

Verywell Health: Is there a specific number of people meeting that could trigger a super spreader event? 

Dr. Robinson: There is no specific universal “safe” number of people for gatherings. This really does depend on the current transmission levels in certain areas and where the attendees are coming from. The CDC lists recommendations for gatherings and events from lowest risk (virtual gatherings) to highest risk (large in-person gatherings without social distancing/masks).

As we move into the winter months, it will become more difficult to have gatherings outdoors, further increasing the risk for SSEs. If you're organizing a small event, keep a list of those that attended. How we choose to spend this time could have a dramatic effect on 2021 and our efforts to eradicate the virus. 

Verywell Health: Are superspreaders usually asymptomatic? How does the incubation period affect the chances of superspreader events? 

Dr. Robinson: The kinetics of SARS-CoV-2 infection appear to enable an increase in superspreader events. We have consistently underestimated this virus. It is much better adapted to us than we originally believed, and the characteristics which we thought would make the virus weaker actually aided in its potency. In part, this is due to the lengthy and variable incubation period—the time between infection and symptom onset.

During the incubation period, an infected individual often doesn’t know they’re carrying the virdus. However, in the case of SARS-CoV-2, this is also the time when the viral load begins to amplify to its peak. This is the riskiest time for infection and contagiousness, and there are often few symptoms to trigger behavioral changes. With the superspreader phenomenon, there is often a 24 to 48 hour period of time during the first week of infection when the viral shedding is at its highest. 

Verywell Health: How do children play a role in transmission? 

Dr. Robinson: The lack of symptoms seen in infected children has led to studies evaluating the effects of pediatric infections on community spread. A recent article from Harvard Medical School shows that infected children had a significantly higher viral load in their airways when compared to severely ill adults in the ICU. Despite the fact that children tend to have lower expression of the known SARS-CoV-2 entry receptor, this does not appear to reduce overall viremia (presence of the virus in the bloodstream).

Additionally, recent studies show that the percentage of COVID-19 cases in children have been increasing, going from an estimated 2.2% of cases in the U.S. in April to 10% in September. This data, of course, has implications for schools reopening and the risk of contagion.

Verywell Health: Can anyone potentially be a superspreader, or are some people more biologically prone to become one than others?

Dr. Robinson: Right now, we don’t know enough to begin to identify who is a potential superspreader either before they’ve been infected or after transmission. Theoretically, there may be predictive features or biomarkers that would allow us to identify individuals or situations that are high-risk. For now, I would say our best tool to prevent SSEs is our personal behavior in preventing situations where SSEs could occur.  

Verywell Health: What are some known outbreaks that have been tied to superspreader events? 

Dr. Robinson: There are now a number of well-publicized SSEs that run the gamut, from a White House Rose Garden event to a hockey game in Florida. The London School of Hygiene and Tropical Medicine has actually put together a database tracking SSEs across the world where you can see this a global phenomenon. I would encourage anyone interested in tracking these issues to visit the site.

Verywell Health: How does contact tracing help with tracking and curbing superspreader events? 

Dr. Robinson: I think contact tracing is a public health intervention that has had untapped potential in the effort to slow the spread of the virus. There are still areas for innovation and improvement that could be game-changing, especially in the setting of SSEs. Early identification of cases and effective contact tracing could limit and potentially control these large outbreaks, but that golden window becomes smaller and smaller the longer we are inactive.

Many states have not been able to fulfill their requests for contact tracers. Since this pandemic has, unfortunately, had dramatic effects on our economy and job loss, there is potential space for some people to pivot into these areas. 

Contact tracing is also a space that could be well served by high-tech solutions. The development of applications to alert those who may have been exposed is another targeted approach worth pursuing. This would allow us to rely less on our memory of events that may have occurred up to two weeks ago. 

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.