Tuesday, June 2 -Wednesday, June 3
We’re hearing more about superspreaders. What is a superspreader? Person, place, or thing? After a survey of articles, I’m beginning to think it’s a combination of all three. It’s not a scientific term. It’s not unique to COVID-19. It doesn’t even have a standard spelling. You will see it in reputable sources written as one word, two words, or hyphenated. But it plays a role in spreading disease and we need to understand how it works.
There is the “typhoid Mary” definition: a “superspreader” individual who infects an unusually large number of other people. Then there is the superspreader event (SSE), a place where a large number of people are infected at, for example, a racetrack or a church. But superspreading is really a combination. An infected individual can become a superspreader if they are at a very contagious phase of a disease AND (a) they travel from place to place, exposing a large number of people along the way, or (b) they expose a lot of people at a single event. The infected individual may or may not know they are sick.
A combination of superspreader events led to the SARS coronavirus pandemic in 2003. One individual in Guangzhou who was hospitalized with severe acute respiratory symptoms infected over 30 patients and staff during 48 hours in one hospital, 21 people in a second hospital, and over 20 friends and family members. If each of those people infected 2 others in the next 48 hours and so on, you can see the impact of a superspreader event. This event along with a few others propelled SARS into the general population.
A recent article (1) describes studies of COVID-19 events outside of China which lead to the conclusion that the disease is not spreading so much through people at random as it is spreading through superspreader events. The conclusion is that 80 percent of COVID cases are spread by less than 10 percent of the total cases and that prevention should be focused on “superspreader events.”
This is borne out by the number of superspreader events in March which are associated with world outbreaks such as Mardi Gras celebrations in Heinsburg, Germany, and New Orleans, megachurch services in South Korea, soccer games and horse races in Britain (2). Not all superspreader events are public gatherings. Some occur in places where people live or work in close proximity to each other, most notoriously nursing homes, prisons, and meatpacking plants. but hospitals can also be superspreader locations especially in the early days before a new disease is recognized.
We’ve heard a lot from epidemiologists about the “R nought” or basic reproduction number, which quantifies how many people the average infected person can infect.(3) With COVID, the number is often given as 2-3. Some countries have succeeded in reducing it to half as many. But if one contagious person at a large event can infect many more than their share, the calculation changes and this changes how we need to manage the spread of COVID. A recent CDC article (4) states that, “SSEs highlight a major limitation of the concept of R0.” because it doesn’t take the variations in transmission into account.
I have a vested interest in understanding the role of SSEs because I am a choral singer and group singing has been implicated in several outbreaks of COVID. In fact the activity of singing itself has been suggested as an effective way to spread virus in droplets. There are anecdotal examples, but is there data? I think it’s important to do more research both because some of the precautions we’re currently taking in public settings may be unnecessary and because we don’t want to give up things like football and weddings and singing and, yes, protests.
Not every large gathering is an equal spreading risk. For example:
- What people are doing may matter more than how many there are. Are they listening to a speaker or concert? Yelling and cheering at a bar or football game? Hugging and laughing after a wedding or graduation? Eating and drinking? Walking around or sitting still?
- How does the setting affect risk? Indoors or outdoors? Good air flow seems to make a difference. Are people walking around in the midst of a crowd or sitting next to the same people for several hours?
- What about the people themselves? Old, young, mixed? Healthy? Joyful, excited, angry, bored, anxious, stressed?
- Does position make a difference–whether you are standing or sitting, facing each other or all facing in the same direction?
- What about environmental factors like lighting or weather or time of day? Dryness or humidity? Altitude? On the grass, on the sand, on cement, on the street, on bleachers?
Retrospective research could be done by looking at past events (and past epidemics) and developing a database to compare them in regard to different variables. This might turn up directions for deeper study. But I think it’s important that we do look into this. Not just because getting together is such an important part of our way of life, but because so many people’s livelihoods depend on things like sports, concerts, performances, graduations, conventions, county fairs, and celebrations.
What can we do to get back into life’s arena?
Today’s Notable Headlines
(2) “Superspreader Events Offer a Clue on Curbing Coronavirus,” Wall Street Journal, June 4, 2020. https://www.wsj.com/articles/superspreader-events-offer-clue-on-curbing-coronavirus-11589977873
(4) “Identifying and Interrupting Superspreading Events—Implications for Control of Severe Acute Respiratory Syndrome Coronavirus 2,” Emerging Infectious Diseases, Volume 26, Number 6—June 2020, CDC. https://wwwnc.cdc.gov/eid/article/26/6/20-0495_article
“70% of people infected with the coronavirus did not pass it to anyone, preliminary research shows. Superspreading events account for most transmission,” Business Insider, June 4, 2020. https://news.yahoo.com/70-people-infected-coronavirus-did-213700577.html
“Do Coronavirus Superspreaders Exist?” Emily Oster, Future Tense, June 1, 2020. https://slate.com/technology/2020/06/coronavirus-superspreaders-do-they-exist.html
Additional Sources for this post:
(1) “Estimating the overdispersion in COVID-19 transmission using outbreak sizes outside China,” Wellcome Open Research, April 9, 2020. https://wellcomeopenresearch.org/articles/5-67
(3) “R0, the Messy Metric That May Soon Shape Our Lives, Explained,” New York Times, April 23, 2020. https://www.nytimes.com/2020/04/23/world/europe/coronavirus-R0-explainer.html
“SARS-CoV: Lessons for global health,” Ralph Steven Baric, April, 2008. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2633111/
Why am I doing this?
The coronavirus pandemic will be indelibly written on our memories just as the Great Depression or the Battle of Britain left their mark on past generations. It is my intention to journal the events of these days from three perspectives: as a retired medical technologist, a historian (Ph.D., 2014), and an ordinary person living through an extraordinary crisis.
You are on History’s Edge.