Meat processing industry: superspreading hot spots

It struck me for the first time a month ago: in the US, workers in the meat processing industry went on strike because COVID-19 had broken out among a number of colleagues. That turned out to be only the beginning, as we now see large numbers of infected workers in the meat processing industry outside the US as well. They form the base for outbreaks in the area around those factories.

There are two components that make these kinds of factories superspreading hotspots. First of all: if you look at photos of those factories, you can see that people are working very closely together.

But I don’t think that’s the only reason that makes COVID-19 strike in meat processing factories. The second reason seems to be that in those factories the temperature is usually kept a bit lower. Not only in storage areas, but also in the rest of the factory. And that creates favorable conditions for micro drops to stay airborne longer and thus contaminate more employees. It is also known that in a colder environment the virus can be found for a longer period of time on, for example, metal. Whichever of the three causes, in combination with each other, every meat processing plant has the risk of becoming a superspreading hotspot.

As a result, in areas of the US where COVID-19 had not yet really broken out and the weather conditions were actually unfavorable for a major outbreak of the virus, it still happened because of the infected workers in those factories.

With the help of Google I came across these outbreaks in the vicinity of factories like this in North America.

If you read the messages, there also seems to be a connection with the type of employees that work in those factories and the way some employers deal with sick people. (Let them come to work anyway).

But also in other countries we see in the media that there are outbreaks at slaughterhouses and meat processing factories:

  • South-Brazil
  • Ireland, waar in het parlement is gemeld dat er verschillende onbekende hotspots in vleesverwerkende fabrieken zouden zijn
  • Birkenfeld, Germany waar veel Roemeense gastarbeiders besmet zijn


In the rest of Europe and in the Netherlands I haven’t really been able to find the kind of outbreaks like in the US. But I don’t know if that means it’s less the case in Europe, or if it’s because it hasn’t been recognized yet that these kind of factories could be hotspots of COVID-19 contamination. Especially in areas where there are already a lot of infestations anyway, it might not be noticed.

This is a website where you can find the locations of those factories in the Netherlands.

It wouldn’t surprise me if this is also the case in Europe. Maybe you know of examples of outbreaks in and around those factories?

Vleesverwerkende industrie: superspreading hot spots

Het viel mij voor het eerst een maand geleden op in de VS: arbeiders in vleesverwerkende industrie gingen in staking omdat COVID-19 was uitgebroken bij een aantal collega’s. Dat bleek slechts het begin te zijn. Lees meer

The spread of the virus is already virtually under control


In this article I show how the COVID-19 virus spread before 15 March, before we took measures in the Netherlands. The overviews per municipality show, that the speed of the virus spreading increased enormously when a so-called “super spread event” was held. Without superspread-events, the virus spread quite slowly. And that even though no measures had been taken at that time. I repeat: none!

After the Netherlands decided on measures around mid-March, we saw in many infected municipalities, that the R0 factor (the speed of reproduction) gradually decreased. Partly due to those measures, but partly also due to the fact that no meetings/events were allowed to be organised.

These findings from the first weeks of March indicate, that the chance of another major outbreak if we mitigate measures is very small. As long as we keep (larger) meetings prohibited for the time being. That is why the government can already take quite a few steps to reduce the measures taken without major risks. I discuss this at the end of the article and give some advice on how we can pick up our lives wisely again without ending up in a 1.5 meter society.

The findings

Below I show you that the COVID-19 virus spreads much less without “superspread events”. This should have major consequences for the exit strategy decision making. Especially because it also shows that the chance of a new outbreak -with the right choice of measures- is virtually nil.

It is important to realize that there are two main ways in which the virus jumps from one human being to another:

  1. A non-infected person comes into close contact with virus droplets, which have escaped from the mouth or nose of a virus carrier. The WHO and RIVM assume that if you stay 1.5 metres away from another person and everyone complies with the instructions on a good personal hygiene, the chance to get infected is very small. In addition, new research shows that the chance that the virus is transmitted via objects is also very small.
  2. An infected person also excretes micro droplets (aerosols). These can remain floating in the air, so that micro droplets from one infected person, can infect many others. In the past month, more and more information has become available about large-scale and small-scale gatherings, where this has happened to a large extent. I call these events “super spread events”. A Canadian journalist has posted an interesting article documenting 58 of these super spread events.

I have already described the effect of the super spread events on the spread of the COVID-19 virus. I described what happened around the Atalanta Bergamo-Valencia’s soccer match on February 19th and what happened after a benefit evening in the Dutch town of Kessel on March 5. But we also know about super spread events in for example Daegu (Korea), Madrid, Mulhouse, Kuala Lumpur and New Orleans (Mardi Gras). And recently I also saw on television that there has been a big New Year’s Eve meeting in Wuhan on 25 January.

The conditions are apparently such that those small particles of the virus can remain in the air for a long time and then infect many of those present. It seems that when attendees sing, the risks are greatest, amplified by poor ventilation and/or low humidity. (Comparable patterns can also be recognized in the case of massive infections of passengers on cruise ships, crew on naval vessels, and in care institutions).

Around 15 March, measures were taken in the Netherlands to slow down the spread of the virus. This means that its effects must be reflected in the figures from 21 March onwards. The previous figures therefore reflect the period in which we were still living together in a normal way. The virus still had free rein then.

Fortunately there are figures available for the development of the number of infections per day per municipality. It is important to realize that the estimation of the number of infected people, all over the world, is a big underestimation of the number of real infections. In the Netherlands, I estimate that in reality the number of people infected is a factor of 50 higher than the test shows. (This is in line with the results of a random survey in LA County). That would mean that by the end of March around 600,000 people in the Netherlands were infected (more than 3%).

Here you will find maps and graphs with figures per municipality. These come from the RIVM and are beautifully processed by the Geodienst in Groningen and the Aletta Jacobs School of Public Health. Based on these figures, I have made the analyses, which you can see below.

So I want to delve deeper into the contamination spread in the Netherlands, before the measures that were taken, had any impact. Because we can learn a lot from when we phase out measures. The number of infections was monitored by the RIVM per municipality until 30 March, so the last 9 days of that month reflect the period that the measures should already have had an impact on the spread of the virus.

R0 is the important factor in a pandemic. The so-called reproduction factor indicates how quickly the virus spreads. The value 2 means that 1 carrier of the virus infects an average of 2 people in 6 days. After 18 days a total of about 18 people would be infected and after 30 days 78. The aim is to bring this R0 below 1. In that case there will be fewer and fewer new infections.

In the case of influenza, an R0 value of between 1.1 and 1.3 is maintained. On COVID-19 the consensus seems to be that the R0 without any measures is somewhere between 2.2 and 2.5. If it were 2.5 then 1 infected person would have infected up to 260 people after 30 days. The RIVM indicates that in the Netherlands, somewhere at the end of March, the R0 had come close to 1 and then went further down.

The big question is of course what exactly the risks are if measures are reduced. The mantra seems to be, that it could go wrong again if we take the wrong step or phase out too quickly. But how big are the risks? That seems to be pure speculation at the moment.

However, there is a way to look more rationally at how big the risks really are. Because before March 15th we just lived a normal life, so the virus could spread optimally. It is only with the observations from 21 March onwards that the measures must have had an effect.

If you then look at the figures from individual municipalities, there are important clues as to what could happen if we were to phase out measures.

Let’s focus on the municipality of Loon op Zand. At the end of February, the first Corona patient in the Netherlands was recorded there. These are the cases per day by 100,000 inhabitants.


(These graphs are the figures per 100,000 inhabitants. For our purpose we are especially interested in the increase factor of the development in time.

At the beginning of March there were 4 virus carriers in Loon op Zand, all in one family. On 21 March there were 14. But even if, as a calculation example, we pretend that at the beginning of March not 4, but only 1 person was infected, that would be more indicative of an R0 somewhere around 1.2.  In the last 9 days of the month, the number of infected persons only increased by a factor of 2. And that also indicates an R0  close to 1.0. (You should always take into account that an infected case detected represents on average 50 infected persons because of underestimation).

Also in the municipality of Altena near the Biesbosch there was already one infected person at the beginning of March.


After 21 days the number of infected persons in Altena stood at 22. This indicates an R0 of 1.2. In the last 9 days the number of infected persons doubled as well. And this also indicates an R0 value close to 1.0.

But how is it that in March the number of infected people in the Netherlands increased exponentially?

I show this by zooming in on a number of municipalities where a super spread event took place. Peel and Maas is a good example. In the village of Kessel (more than 4,000 inhabitants) there was a benefit meeting with more than 300 people on March 5th.


The event was on March 5. On March 11 the first infections in the municipality were registered and on March 21 there were already 63.  So in 10 days the number of infected people has increased significantly. Based on the underestimation of the number of people actually infected, that would mean that on March 21, 16 days after the event, more than 3,000 people in that municipality (with a centre of gravity in Kessel) had already been infected.  This is an R0 that is significantly above 5.0. However, between 21 and 30 March, the number of infected persons in this municipality increased by just over a factor of 2. And that resembles the figures of Loon op Zand and Altena. So the effect of the measures taken around March 15th!

While in Peel en Maas the super spread event of March 5th was the starting point of the big outbreak, in Uden it was Sunday March 1st. We can see that in the graph below. Almost certainly someone was present at one or more church services who was infected at that time and sang along.

The first infection was detected on March 6th. On March 21 the number of infected persons in Uden was 76. An increase in 15 days by a factor of 76. That too is an R0 that is far above 5.  And also in Uden we see that between 21 March and 30 March the increase was only a factor 2. So an R0 that came close to 1.0.

Emmen is a municipality, which has an even slower spread than Altena. On March 8 the first infection was detected and only 4 on March 21. So without any measures in Emmen with 100,000 inhabitants there was only an R0 of just over 1.0 !!!

Here we see in the last 9 days a somewhat larger increase than in the other municipalities. It increases by a factor of 3.5. At the end of the month Emmen (via that multiplication factor of 50) had an estimated 0.7% infected persons in the municipality, whereas in Uden it must have been 15% already.

Also when we look at other municipalities it is striking that in quite a few municipalities we recognize the influence of super spread event. Church services on March 1 and 8 and the “afternoons for the crop”celebrations on 11 March seem to qualify as super spread events in those congregations. But I have also been notified of outbreaks of the virus after choir rehearsals or – performances.

Below is a selection of these municipalities:


For comparison a number of municipalities that already had an infection in the first 10 days of March, but where the spread was much slower, apparently because no super spread event had taken place.


If you look at the development in larger municipalities, with 5 to 20 times more inhabitants than those small ones, then by the law of the large numbers it becomes a mix of superspread events and the “normal” spread from person to person. And you can’t recognize them separately anymore.

In Tilburg (not far from Loon op Zand) the first infection was on March 1st. On March 21 the number was 154. That indicates an R0 of over 4. It is very likely that also in Tilburg between March 1 and 8, through church services, choir rehearsals or parties, super spread events took place.

Between March 21 and 30 we also see an increase of only a little more than the factor 2 in Tilburg. Breda shows, with a delay of a few days, the same pattern as Tilburg.

If you only look at the total figures in the Netherlands per day, you can see an exponential growth until the end of March. But if you look at the municipalities separately, you see a much more nuanced picture. While in most municipalities where the virus had been circulating for some time, the increase between 21 March and 30 March was only around a factor of 2, for the whole of the Netherlands it was a factor of 2.8. And that’s because on mid-March there were still 120 municipalities where no infection had yet been detected and most of them only got going in the last part of March.



The study of the development in the municipalities between March 1 and 21, shows that super spread events, when no measures were in place, led to a very sharp increase in the number of infections. Without these events and without any measures such as social distancing and banning visits to the hospitality industry, hairdressers, manicures, etc., the R0 seems to be somewhere between 1.1 and 1.5. A value that resembles that of influenza.

In this blog I have explained why in case of flu epidemics, we cannot easily recognize the influence of super spread events. But with COVID-19, with no historical immunity among the attendees, you immediately notice a week after the event that it had a major impact.

If we were to live our lives again, exactly as we did before 15 March (something I absolutely do not advocate) and we would only forbid meetings of more than 3 people, then the R0 alone would drop to a value of around 1.2 to 1.3. For the record, that’s just by living our normal lives as we did before March 10 and certainly not as a “1.5 meter society”!

The Israeli chairman of the “National Council for Research and Development”, a mathematics professor, noted that a similar pattern can be recognized all over the world.  The first 40 days an increase and then a decrease. Which he indicated seemed to come to zero after a while.

In discussions he indicated that he had no explanation for this, but found it remarkable, that it seemed that the measures governments had taken, or not taken, had little influence on that curve. Wherever he looked, he saw more or less the same pattern, also in a country like Sweden.

My analysis is the missing link in this professor’s finding. Because there is one measure that has been taken almost everywhere in the world:

Prohibiting meetings with a larger number of people.

Virtually all countries have, in addition to the measures they have taken (from a complete Lock down, via an intelligent Lock down, to a somewhat freer approach like in Sweden), decided that ‘super spread events’ can no longer take place. This alone has considerably slowed down the spread of the virus. The other measures taken by governments, push the R0 (well) below 1 and that is the image that the Israeli professor saw all over the world.

This should have major consequences for the exit strategy of governments worldwide and certainly to the Dutch!

As long as the meetings with a larger number of people remain forbidden, there is no chance that there will be another major outbreak of the virus “which will undo all our efforts” as Premier Rutte said, at the intercession of the Outbreak Management Team members.

We could already take steps now, which will keep the chance of new infections smaller than in many low infected municipalities before March 21 this year.

Of course with a smart policy. Just like Germany mandatory mouth protection in public transport and shops would already be a good step away from the completely unnecessary 1.5 meter society, as I have shown above. Making hairdressers, manicures, pedicures, beauticians (with mouth guards) work again can be done without any objections. Also the hospitality industry could start up again. Especially venues with outdoor terraces. But also others, with some extra facilities inside.

I also think that it will be proven, that wearing mouth protection anywhere outside also means that we don’t have to keep a 1.5 meter distance. East Asia shows us the way. And in Jena in Germany they have been doing that for some time with very good results.  But if we don’t want to / can’t do that yet, then the 1.5 meter distance (except in public transport and shops) is still a good choice. And older people are indeed the most vulnerable and they should be more cautious for the time being. (Here, too, mouth protection for the elderly themselves and their visitors is a wise choice).

A number of other important lessons have been learned from those super spread events. Which we still have to apply as long as the COVID -19 virus is still present.

It is evident that in confined spaces where foreign people gather, the risk of the virus spreading via aerosols is greatest. Good ventilation and an air humidity of 45% at 20 degrees Celsius is an extra precaution against this spread via aerosols.

In offices, care institutions and schools, the way in which internal ventilation and heating/cooling is regulated is a risk factor. Here too, there are clear indications that aerosols spread via these types of systems if they are not properly regulated. How do you think that 900 people got infected on a naval vessel? Not because all those 900 people have moved within one and a half metres of an infected person. No, it’s mainly because of those floating aerosols.  The same risk was/is also present in care institutions. Usually little fresh air ventilation. Where many people are infected in a care facility, two causes are most obvious: church service and festive evening with many residents of the facility, or the internal heating/ventilation system.

Although it is undoubtedly true that children are less vulnerable to the spread of COVID-19, a day at school could also turn into a super spread event.  To avoid this, schools should do the following:

  • Ventilate as much as possible and teach in the open air if possible.
  • Bring the air humidity in the building to the level of 6 g/kg (that’s about 45% relative humidity at 20 degrees Celsius). Here you can calculate this value.
  • If the ventilation and/or air circulation or humidity inside the school is not good, use mouth protection.
  • And certainly stop singing in classes.

On that basis it is very well possible to keep a good balance between public health and the importance of the economy and society.

We have to get rid of the unfounded fear that the virus could re-erupt at any moment, when we know that we have banned the biggest source of the spread, the super spread events. Let’s use the energy together to start up society again quickly and smartly on the basis of good analyses and data and not on the basis of empty cries.

Last but not least, there are many indications that as it gets warmer and more humid, the spread of the virus will be further slowed down, including in this research by Homeland Security’s lab in the US. Not that the virus will disappear completely. In the autumn these conditions will become more unfavorable again. But then we have already learned a lot more (at least that should be the case), in order to prevent a large spread of the virus, as it has happened for the last month and a half.

The superspread event on March 5th in Kessel

The municipality of Peel en Maas is the municipality with the most hospitalizations in the Netherlands. TV newscast EenVandaag devoted a report to it on 19 March.

A meeting on 5 March in community center De Poart in Kessel was the superspread event for the outbreak there. The available data give a good impression of the impact of that event. It was a meeting to raise money for the muscular disease of a fellow villager.  This is the report that broadcaster P&M made of it. Here we see a picture of another meeting in that community center, which gives an impression of what it looks like inside.


And this is a photo taken at the actual event.

It’s not really a large venue. There would have been 500 people present, most of them from Kessel. A village with 4,000 inhabitants in the municipality of Peel en Maas. From the video it is clear that people of all ages were present. Through the weather information for that evening we have determined that the specific humidity was 5.8 g/kg.

In this blog I will have to make several assumptions, because the specific numbers for the village of Kessel are not known. Plus we also know that the number of deaths and infections in the Netherlands are underestimated. But there is a very important reason why I do the following.

First I show the estimated figures, to give an impression and then I come to an important conclusion.

In March, the RIVM recorded the number of infections per municipality. These are the figures for the municipality of Peel and Maas until the end of March: 310 infections per 100,000 inhabitants.




In the meantime, this number has risen to 550 with the note that because relatively few tests are carried out in the Netherlands, the actual number of infections can be a factor of 15 to 20 times higher. This could therefore mean that the percentage of infected people in this municipality is 8 to 11%.

In terms of population, Kessel is one tenth of the municipality of Peel en Maas. But it is clearly the source of the wildfire in that municipality. In the adjacent municipality of Horst aan de Maas we see figures that are one third of the municipality of Peel en Maas. If we assume that the municipality of Peel en Maas, excluding the village of Kessel, has the same figures as Horst aan de Maas, this would mean that at least half of all infections of the municipality of Peel en Maas have occurred in the village of Kessel. And that would mean that by the end of March, the proportion of infected people in Kessel must have already reached 2,000, which is 50% of the population!

Since then, the number of victims in that municipality has only increased. And that’s interesting because Peel & Maas seemed to be on its way to reap the benefits of the group immunity strategy initially propagated by Dutch Prime Minister Rutte.

Since April 1st, the RIVM only displays the number of hospital admissions per municipality. And these are the figures for Peel and Maas. At the beginning of the month the number was around 220, and on April 19th, 310 per 100,000 inhabitants.




The number of deceased inhabitants of this municipality is 56 on 19 April (129 per 100,000 inhabitants). This puts the municipality in 6th place in the Netherlands. Boekel has almost 200 per 100,000 inhabitants. (Experience shows, based on CBS civil registry counts, that there is an underestimation of about 100% of the number of COVID-19 deaths. So maybe the number of deceased in this municipality is double as well).

With all this information, it is now possible to give a picture of the result of this super spread event.

There were several hundreds present. It can be assumed, that there were people present who were infected during Carnival 2 weeks earlier, without realizing that they were infected.

10 days after the event in Kessel, the municipality had 30 “officially” infected people. However, taking into account the underestimation of the infected cases, I estimate that at that time around 300 people in the municipality were already infected. That would mean that 75% or more of those present had become infected that evening.

According to the regular course of the spread, each infected person may have infected another person after about 7 days. So even without a super spread effect, 50% of the inhabitants of Kessel could already be infected by the end of March. It is also interesting whether church services were held between 5 and 20 March and whether they also led to additional infections. After 23 March the rate of the infections decreased considerably due to the announced measures.

Considering the given numbers, the number of Corona deceased in Kessel seems to have been somewhere between 40 and 60. (The pastor mentioned in the report of EenVandaag the number of 30, but I don’t know if any people died in Kessel who were not buried at the church.) It is also well possible that there are still people in Kessel who are very sick and may still die.

I estimate that at the super spread event on March 5th in Kessel about 50 to 75% of the people present were infected with the virus. And that in the following weeks between 40% and 60% of the municipality was infected. (That would be 1,600 to 2,400 people). This now leads to 40 to 60 deaths. 10% of the inhabitants of Kessel are over 75 years of age. The mortality risk of infected elderly people is significantly higher than that of people under that age. (75% of all deceased people in the Netherlands are over 75 years of age!). It seems not unlikely to me that a similar pattern is visible in Kessel.

This gives a good impression of the enormous effect of the super spread event on 5 March in Kessel, even if the actual figures would be a bit lower.

Last but not least: Precisely because the number of infections and casualties in Kessel has been so high and it is also certain that there was a super spread event, I would urge the RIVM and the Ministry of Health, Welfare and Sport to start an investigation in the municipality.

I would like to know of all the victims (dead and infected) whether they have been at that meeting on 5 March and, if not, whether someone from their families has been there. In addition, I would carry out a random sample survey of approximately 500 people in Kessel to determine how many people were found to be infected.

I would also take a questionnaire to establish whether they had any complaints and if so, which ones and for how long. Whether they have been at that meeting on 5 March, or whether they had had contact with people who had been there. Did they visit church between 5 and 20 March? Plus I’d like to find out when the complaints started and when they ended.

Doing so will provide a wealth of information about all the facets of the spread of this virus and also what is actually the maximum percentage of people that can be infected.

I would say, do it as soon as possible.

That’s how big the impact of super spread events is

I have already indicated that there are apparently certain events where someone who is infected without even knowing it, infects a lot of others at once. While the image given so far is that these are “super spreaders”, i.e. persons who, for one reason or another, infect many others, I think that these events are occasions where the conditions of super spreading are optimal. I call them “super spread events”.   Many events have been identified worldwide. All in the course of February. For example, a church meeting in Korea, an Islamic multi-day event in Malaysia, a Christian multi-day event in France and Mardi Gras in New Orleans.

In addition to these large-scale super spread events, there have also been many smaller scale super spread events. Meetings where significantly fewer people were present, but a large part of the attendees have become infected. (Through the spread of the virus through micro-drops.)

These have for example been church services, choir rehearsals, or events around football matches. It seems, that where many people sing or talk in an enclosed space, one infected person can be responsible for the contamination of many by the emission of infected micro-drops. And under unfavorable conditions (poor ventilation and low humidity) these micro-drops remain floating for a long time.

In Brabant-Limburg (The Netherlands) Carnival seems to have been a super spread event where many people got infected at the same time. (I don’t think so much outside during a parade, but just inside cafes and other festivities). If you look at the graph of the Netherlands of the number of deceased you see that Limburg and Brabant had to suffer significantly more deaths per inhabitant than the other provinces.

A similar graph can also be made for Italy.

In this graph I show a number of Italian regions and Dutch provinces until the 36th day after the 10th infection in that province.


But if you look at Lombardy, you have to realize that the province has 10 million inhabitants and the source of the wildfire was in the three regions around the town of Bergamo.  Half of the cases emerged there, although that city/region only counts for a quarter of the inhabitants of Lombardy. So the death toll per inhabitant in that area is about twice as high as shown on this graph. Also in Brabant and Limburg there is a considerable difference by part of the province, as this map shows the number of deceased persons per 100,000 inhabitants. (You can also see the Dutch Bible belt in this chart. The diagonal from Goeree-Overflakkee to Staphorst. The super spread-events there have been the church services like the “afternoon for the crop” of March 11th).

But of all the super spread events in Europe, the Atalanta Bergamo – Valencia soccer match must have been the biggest. (Partly due to the fact that that area around Bergamo is such a clear “frontrunner”).

To understand how such a super spread event works and what the consequences are, I zoom in on that race. It took place in Milan on the 19th of February.

I suspect that the spread actually took place in the stadium (in open air), but also in venues where large groups gathered in relation to the match. For example, the large numbers of supporters who went to Milan from Bergamo – often by coach – and celebrated before and after the match, and the groups of people who watched the match together in indoor venues like bars etc. around Bergamo. That evening the specific humidity in that area was also around 4.5 g/kg.

Figures including some assumptions from the Bergamo region give an impression of what may have happened then. They clearly illustrate how much impact these meetings have on the spread of COVID-19. Here the specific figures from the provinces within the Lombardy region, three of which are around Bergamo.

The first outbreaks were in the province of Lodi (with over 200,000 inhabitants) and the province of Bergamo (with about 1 million inhabitants). Shortly afterwards the province of Brescia followed with 1.2 million people.  These three provinces are home to 25% of the inhabitants of Lombardy and inhabit half of the infected persons of Lombardy.

The first cases of COVID-19 were recognized around 15 February. The clothing and footwear industry in Italy has largely fallen into Chinese hands, so it could just be that these infections arose after Chinese New Year on 25 January. In the first half of February people undoubtedly returned from China, some of them carrying the virus.

When the soccer match in Milan took place on 19 February, people were already infected in the area around Bergamo. I’m trying to estimate the real number of infections based on the number of people who died on average 18 days after the event. I multiply the number of deaths by 200 to estimate the total number of infected people. (This is based on extensive research by Prof. Streeck in Kreis Heinsburg).

On the basis of that conversion, there must have been about 3,000 infected persons in the Bergamo region by 19 February. That is 1,500 per 1 million inhabitants.

If we now count the deaths in that area from 2 to 4 weeks after the match, then one week after the match there must have been around 60,000 infected persons in that region.

Without this super spread event, the number of infected persons would have risen from 3,000 to around 12,500 in a week based on the normal R0 (reproduction factor) for this virus. But it would have been almost 50,000 more.

Let’s assume that 250,000 people in larger groups watched the match in the stadium and indoor venues like bars etc. On the basis of those 1,500 per 1 million, almost 400 of them would have been infected. On the afternoon and evening of the match they infected 50,000 other people, an average of 125 per person!

In the province of Lodi, heavy measures have already been taken at the end of February. In the province of Bergamo that happened on March 8th. The effect of this can be clearly seen on the graph below, reflecting the established cases. The actual number must have been at least 50 times higher around March 3.


Around 20 March, the new number of deaths in Lombardy (including Milan) peaked at over 500 per day. After that it remained stable for a while and now we see a decreasing trend with about 300 deaths per day.

This numerical effect – despite the necessary assumptions – gives a good impression of both the effect of super spread events accelerating the speed of the spread, and the impact of harsh measures to contain the virus.

At the same time, it teaches us that if we do not organize these kinds of events for the time being (i.e. no church gatherings either), then the R0 (the spread factor) alone will quickly fall further.

The biggest challenge will be to slowly start normalizing society (with the new normal) on the one hand, and on the other hand to see how we can also organize meetings where many people are present.

More knowledge about this will be able to ensure a balanced approach. The risk of a super spread event in the open air may turn out to be small. And it might be advisable to only hold indoor meetings with mouth protection and/or increased humidity. Prof. Streeck’s research in Heinsburg is very important in this respect.

With regard to the approach to the exit policy, these are very important questions to answer quickly.

Het superspread event van 5 maart in Kessel

De gemeente Peel en Maas is de gemeente met de meeste ziekenhuisopnamen in Nederland. EenVandaag besteedde er op 19 maart een reportage aan.

Lees meer

Daarom kenden we de superspread events niet

Bij de snelle verspreiding van het COVID-19 virus spelen de “superspread events” een grote (zelfs cruciale) rol, zoals ik hier ook uitleg. Maar waarom kenden we die dan niet eerder bij influenza (griep)?

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