Super Spreading Event: You are the winner, and you are the loser?

Original author: Dyani Lewis non-uniform mode of transmission of the virus has brought new crown tragedy, but also provides inspiration for targeted prevention and control.

On December 5th last year, on the eve of people celebrating the traditional Christmas festival, the Hemelrijck nursing home near Antwerp, Belgium invited Santa Claus (Sinterklaas) to join the fun.

However, this celebration event ended in tragedy-well-dressed volunteers inadvertently spread the new crown virus to 40 employees and more than 100 elderly people in nursing homes.
At least 26 people have died.
These volunteers later also Tested positive.

Such super-spreading incidents generally involve a situation where one person infects multiple people at the same time, which is not surprising now.

Such dangerous infectious incidents have occurred in choir rehearsals, funerals, family gatherings, and fitness classes.

Crowded indoor places such as restaurants are a high incidence of super-spreading incidents.
In such incidents, one person can transmit the virus to several people.

Source: Aaron Lavinsky/Star Tribune/Getty Akira Endo (Akira Endo) is an infectious disease modeler at the London School of Hygiene and Tropical Medicine.
He noticed the super-spreading incident before it became a "frequent visitor" to the new crown report Red flags.

Endo said that the earliest signal came from an incident in which ten people were infected by one person [1], and that there was no suspicious incident that caused a large-scale disease outbreak in the area outside Wuhan.

Endo was one of the first scientists to quantify the phenomenon of super spread.

In this spatter-like non-uniform spread, most people are infected by a small number of infected people.

The viruses that also have this mode of transmission may be SARS-CoV and MERS-CoV, the cousins ​​of the new coronavirus.

SARS-CoV caused the fatal epidemic of severe acute respiratory syndrome (SARS) in 2003, and MERS-CoV caused the Middle East respiratory syndrome.

Pathogens that cause Ebola, smallpox, and tuberculosis also have similar transmission patterns.

The new crown epidemic has entered its second year, and this time there are more new variants that spread faster, but researchers are more convinced than ever that the super transmission event has played an important role in determining the history and future direction of the new crown epidemic.

The new crown virus has currently infected more than 100 million people, with more than 2.
4 million deaths (as of February 23, 2021).

Researchers have found that super transmission events are one of the main ways for the new coronavirus to form a transmission chain in the community.

If there is no effective prevention and control method, as mutants with stronger transmission power than those originally discovered in the United Kingdom, South Africa, and Brazil are discovered in various places, super transmission events may be larger and more frequent than the current ones.

With data for a whole year, researchers have sufficient evidence that the main factor in the occurrence of super-spreading incidents is long-term gathering in poorly ventilated rooms.

Singing and aerobic exercise are also common factors, and these activities produce many infectious tiny particles that can be inhaled by others.

However, the key issue has not been resolved.

Endo said: "We already know what factors will play a role, but we don't know what is the main cause of the super-spreading event.

" The biggest uncertainty is the extent to which individual behavioral and biological differences play a role.
Role, or controllable, and how to avoid high-risk scenarios in a targeted manner without causing social shutdown.

It is crucial to understand the cause of the super-spreading incident, said Lucy Li, an infectious disease modeler at the Chen Zuckerberg Biological Center in San Francisco.

Experts say that now that we have clarified the main factors that induced the super-spreading event, we should take corresponding actions now.

They called on decision makers to turn their existing knowledge into targeted prevention and control measures that can alleviate or even eliminate the epidemic.

One of the most fundamental means is to close crowded indoor hot spots to prevent super-spreading incidents from happening.

The researchers also recommend adopting the Japanese approach to reproduce the super-spreading incident through reverse contact tracing.

On average, outbreaks of sexual transmission can infect 2 to 3 people per person infected with the new coronavirus.

This rough estimate of the population level is also called the basic reproduction number (R0), but this number smooths out the huge differences between individuals.

In reality, most cases of infection actually come from a small group of people (see "Infection Contact Map").

Endo’s early analysis estimated that as of the end of February 2020, about 80% of second-generation cases in countries outside of China came from 10% of infected persons [2].

Source: K.
Sun et al.
Science 371, eabe2424 (2021) estimated data from Israel, India, Hong Kong and other places in China to support this observation.

Although this mode of transmission also exists for other infectious diseases, it is particularly prominent in the new crown epidemic.

In contrast, the individual differences in influenza are not so great, Endo said, the spread of influenza is more even.

Li said that the outcome of the super-spreading incident is that a small number of infected cases will quickly spiral out of control.

Li's research is about super-spread phenomena in the United States, Europe, and China.

"If a super-spreader chain has been formed, the number of cases will surge in a short period of time.

" She said.

In addition, variants found in the United Kingdom, South Africa, and Brazil will also exacerbate super-spreading events, Li said.

It has been reported that the transmission rate of the B.
1.
1.
7 variant strain is 50% higher [3], "This may make the super transmission event higher in frequency and scale.

" She said.

Bronwyn MacInnis, a geneticist at the Broad Institute of MIT and Harvard University, led a team that used viral genome sequences to track the impact of super-spreading events.

One of the incidents was a two-day international business conference held in Boston at the end of February 2020.
This conference caused 90 participants and their close contacts to be infected [4].

However, the real impact of this incident goes far beyond that, MacInnis said.

She estimates that about 20,000 infections in Boston and its surrounding areas can be traced back to this meeting.

Do super spreaders exist? Although most cases are infected by a small number of people, researchers still don’t know whether there are biological factors that make these people easy to spread the virus, such as some people’s natural voices, or some people’s lung capacity when they exhale.
.

The physicist Christian Kähler studied the production and dynamics of aerosols at the Bundeswehr University in Munich, Germany.
He believes that these people may be born to produce more aerosols-aerosols are tiny particles that carry viruses that spread in the air.
.

In addition, women and children have smaller lung capacity than men and produce fewer aerosols.

However, he and some researchers questioned whether there are other biological differences.

"The super aerosol communicator hypothesis is a bit too simple.

" He said.

Kähler believes that personal behaviors, such as their inability to maintain a safe distance from others during conversations, or their refusal to wear masks-these behaviors are more likely to increase the risk of transmission than the aerosol volume they generate.

Singing and speaking loudly can also increase the aerosol produced, he said.

According to a study that has not been peer-reviewed [6], the number of particles produced by loud speech can be up to 50 times that of normal speech [5], and singing can be up to 99 times.

Differences in the immune response between individuals can also affect the amount of virus a person produces, said Dominic Dwyer, a virologist at the Health Pathology Centre of New South Wales, Australia.

The difference in the response of children’s immune systems to infections is believed to be the reason why children’s infections and transmission of new coronaviruses are not as frequent as adults [7].

Dwyer said it may be because adults have a full spectrum of immune responses.

At one end of the lineage, “immunosuppressed patients usually excrete more virus and last longer.

” He said.

A Thai restaurant with the theme of "Airplane Cafe".
This concept is so popular because many people reduced their trips last year.

Some studies have shown that a large part of the spread of the virus comes from such crowded restaurants.

Source: Mladen Antonov/AFP/Getty recently published a study that analyzed the aerosols produced by 200 healthy people [8].
The results support the view that biological differences may affect the spread of the virus.

The study estimated that 20% of participants produced 80% of aerosol particles, and that the elderly and overweight people produced more aerosols than the average person.

However, researchers who use mathematical models to track outbreaks believe that biological differences do not need to be included to explain super-spreading events.

In a study that has not yet been peer-reviewed [9], Harvard University physicist Mara Prentiss and her colleagues analyzed five super-spreading events in order to clarify how many virus particles an infected person can produce.

Although these incidents were very different-one occurred in the spacious call center, one occurred in the sports class, two occurred on the bus, and the last one was the choir rehearsal-the amount of virus produced by the infected individual was unexpected.
The ground is quite.

"We were a little surprised," Prentiss said, because it shows that in super-spreading events, the impact of individual differences is very small.

In the few cases that Prentiss and her team studied, the people most likely to infect others either had mild symptoms or had not yet developed symptoms.

This similarity is critical and may also occur in other super-spreading events.

"The transmission among young, healthy, and mobile people is actually the most dangerous," MacInnis said.
"Just because you feel good does not mean that you are not infected or potentially infectious. "She said.

Although the mode of transmission may not have much to do with the biological differences between individuals, the behavioral differences between individuals are not the same.

In work and life, you have to contact a large number of people or people who are more socially gregarious.
It may be easier to become a super-spreader than those who are not so gregarious, Kähler said.

Problem sites In the past year, an important lesson that people have summed up is that places where people gather are directly related to the risk of infection.

Numerous super-spreading incidents have occurred.
Indoors
with poor ventilation.
This is consistent with other existing evidence that airborne transmission through aerosols is an important or main mode of human-to-human transmission of the new coronavirus.

Japan has discovered this problem early in 2020.
In February 2008, people were reminded of the “3Cs” that increase the risk of infection-closed spaces, crowded places and close-contact settings.
The
World Health Organization’s Western Pacific Region adopted it in July 3C precautions.

Limiting the number of people gathered indoors has become a major public health measure for global epidemic prevention and control.

Researchers also want to further clarify the exact factors that constitute high-risk indoor environments, so as to improve the pertinence of restrictions and reduce their destructiveness.

Stanford University computing scientist Jure Leskovec and his team used crowd movement data to analyze which places are at the highest risk.
The
research team used anonymous mobile phone location data to simulate the hourly movement of about 100 million people in the United States between March and May last year.
.

simple assumption Leskovec make is smaller, more crowded, the greater the longer opening hours of workplace risk, and finally he found restaurants, cafes, gym belong to the spread of hotspots [10].

he said, 10% of the sites contributed 80% of predicted infection cases.

Leskovec's model can also explain to a certain extent why low-income communities are particularly affected by the epidemic.

In the face of lockdown measures, the movement of residents in low-income communities has not decreased as much as that of residents in high-income communities-this may be due to the nature of work, but the risk of infection in low-income areas has increased.

Shops are more crowded and people stay in shops for longer.

Leskovec said that simply because of differences in personnel mobility, “low-income individuals are about twice as likely to go to a store once as others.

” These differences may explain why the infection rate observed in these communities is higher, he said.
Said, it also reminds us that resources such as publicity and education or masks may help curb the spread of the virus in such communities.

Max Lau, a disease modeler at Emory University, also used mobile phone data to study transmission dynamics [11].

By calculating the spread of the virus in parts of Georgia—represented by the spread parameter k—he compared the probability of super-spreading events in different populations.

The smaller the value of k, the more concentrated the spread, and the more likely the super spread occurs.

Lau found that super-spreading incidents are particularly prominent among work and social groups under the age of 60, and it is also an important incentive for the spread of the virus in the suburbs.
This may be because it is more difficult for the suburbs to comply with the "shelter-in-place" policy.
He said.

Using super-spreading incidents As we have a deeper understanding of super-spreading incidents and their role in promoting the spread of the virus, our prevention and control countermeasures can also be targeted.

One of the countermeasures is to focus on tracing contacts to find and alert people who may be at risk of exposure.

In February last year, Japan successfully implemented this strategy called "aggregated reverse contact tracing.
"
Reverse contact tracing does not follow the development of time to find close contacts who may have been exposed to a specific individual, but reverse the transmission chain to find the infected person who has infected this person in the past.

Newly-emerged infected persons are more likely to have been infected during a super-spreading event, rather than someone specifically passing the virus to them.

Therefore, contact tracing can easily detect super-spreading incidents in this way.

Endo’s simulation shows that reverse contact tracing has a considerable effect on the control of the epidemic [12].

However, this type of contact tracing requires a lot of manpower and is only suitable for use when the number of cases has been reduced.

In this case, "reverse tracking is very useful and can be the last hammer to end the epidemic.

" Endo said.

Ideally, public health measures should prevent the occurrence of super-spreading incidents at the source.

But MacInnis believes that when the number of cases starts to surge, it will be especially difficult to find out some details of the super-spreading incident-the United States, the United Kingdom, and most of Europe have recently encountered this situation.

 Leskovec's research suggests a way to control transmission.

By simulating multiple communication scenarios, he found that 20% of the communication events one month after the store reopened came from restaurants.

This shows that restaurants are particularly risky and should be controlled instead of closing all businesses.

Leskovec is currently discussing with decision makers how to use his model to fine-tune the resumption of work policy, so as to maximize the effect of epidemic control and minimize the damage to businesses.

But Li said that not all risks can be easily ruled out.

Those basic workers who will have close contact with others will continue to be in high-risk environments, such as meat processors.

"The potential risks of super-spreading incidents will continue to exist because of the structure of social operations,
" she said.

At the beginning of this year, some countries encountered the most severe transmission incident so far.

With the more contagious mutant virus spreading around the world, the epidemic seems to be out of reach.

However, when the epidemic finally begins to ease—whether because of lockdowns or vaccination—super-spreading events will also account for a greater proportion of new cases, Lau said.

This shows that it is particularly important to continue to comply with epidemic prevention measures, even when the number of cases is low.

"If we see the number of cases start to decrease, we must be more vigilant about super-spreading incidents,
" he said.

References: 1.
Liu, Y.
, Eggo, RM & Kucharski, AJ Lancet 395, E47 (2020).
2.
Endo, A.
et al.
Wellcome Open Res.
5, 67 (2020).
3.
Volz, E .
et al.
Preprint at medRxiv https://doi.
org/10.
1101/2020.
12.
30.
20249034 (2021).
4.
Lemieux, JE et al.
Preprint at medRxiv https://doi.
org/10.
1101/2020.
08.
23.
20178236 (2020 ).
5.
Asadi, S.
et al.
Sci.
Rep.
9, 2348 (2019).
6.
Mürbe, D.
et al.
Preprint at https://doi.
org/10.
14279/depositonce-10375.
3 (2020).
7.
Viner, RM et al.
JAMA Paediatr.
175, 143–156 (2021).
8.
Edwards, DA et al.
Proc.
Natl Acad.
Sci.
USA 118, e2021830118 (2021).
9.
Prentiss, M.
, Chu, A.
& Berggren, KK Preprint at medRxiv https://doi.
org/10.
1101/2020.
10.
21.
20216895 (2020).
10.
Chang, S.
et al.
Nature 589, 82–87 (2021).
11.
Lau , MSY et al.
Proc.
Natl Acad.
Sci.
USA 117, 22430–22435 (2020).
12.
Endo, A.
et al.
Wellcome Open Res.
5,239 (2021).
The original article was titled Superspreading drives the COVID pandemic — and could help to tame it.
It was published on February 23, 2021 in the news feature section of Nature.