Covid-19: What is a super spreader event?
- A super spreader event happens when a single infected person spreads a disease to more than eight people.
- Mass gatherings have played a big role in the spread of the coronavirus.
- These events include religious gatherings, birthday parties and even funerals.
At the beginning of the 20th century, an Irish cook spread a vicious disease to 56 people in New York City. She later became known as "Typhoid Mary".
This is known as a super spreader event (SSE), where one infected person ends up spreading a disease to a large number of people, often unknowingly.
More than a hundred years later, the world is in the grip of a massive pandemic, and one of the biggest drivers of its global spread is SSEs.
During February, the Centres for Disease Control and Prevention (CDC) reported that the number of coronavirus cases in the US was low and "appeared contained", but by the end of the month events like Mardis Gras, an international work conference in Boston and even a funeral in Georgia had spread the disease far and wide.
In South Africa, similar events also contributed to the spread, creating virus hotspots. A prayer breakfast in Bloemfontein led to a massive increase in cases in the Free State due to five infected international travellers.
In East London, a woman who attended a funeral spread the virus in a correctional facility, while a massive outbreak shut down a hospital in KwaZulu-Natal.
But how do you define a super spreader event?
According to a paper from Nature that analysed viral spread, disease transmission generally works on a 20/80 principle – 20% of infected individuals are responsible for 80% of transmissions.
A SSE, in this case, takes place when an infected individual spreads a disease to an unusually large number of secondary cases. Without mass gatherings, an average person's infection rate is quite low.
Infection rate varies
Another paper that focused on the spread of SARS published by the CDC defined a super spreader as someone who has transmitted the disease to at least eight contacts.
In the SARS virus' case, one SSE linked to its spread was an ill traveller in a Hong Kong hotel from where it spread to other countries through international visitors.
They concluded factors that influenced the spread of SARS included the host, the agent and the environment.
Another review on SARS studies from ScienceDirect also found that in the absence of SSEs, most individuals infect few, if any, secondary contacts.
With Covid-19, medical professors told CBS News an SSE also depends heavily on how contagious the infected individual is while attending a mass gathering.
They added, however, that it's difficult to ascertain the average infection rate for Covid-19 because it varies between those who put themselves in quarantine at the first sign of symptoms and those with no symptoms attending large events.
Unfortunately, a Chinese study published in NatureMedicine found that with this, coronavirus infected people can be highly contagious before they even show symptoms, which is why a super spreader could be completely unaware of their status.
What are the makings of a super spreader event?
A Canadian journalist from Quillette analysed 58 well-documented Covid-19 SSEs to see if any common traits made up these mass gatherings.
Large-scale liquor consumption
These events tend to take place indoors, where people are in close proximity to each other for an extended period of time with intense face-to-face conversations.
The probability of breaking out into song is another factor that was interesting, as this helps spread the virus into the air.
Outside of hospitals, old-age homes, and cruise ships – where the risk factors for an outbreak are high – many of the events shared some similar markings. Religious services and events made up a big part of the SSEs, as well as weddings and funerals.
Any event with large-scale liquor consumption was another popular SSE, like birthday parties, festivals and concerts.
Another category included business meetings – especially international events that helped drive the global spread in the beginning.
The best way to avoid SSEs is quite obvious. Avoid massive gatherings completely, and if you do attend, wear a face mask and administer strict physical distancing – basically the opposite of US President Donald Trump's rally in Tulsa.
So opt for a Zoom call instead.
Image credit: Pixabay