Another substandard Dutch study on aerosols

Summary of the article

A Dutch study on the spread of the virus in schools, where ventilation does not appear to have an effect, is qualified in the US as below average. In those 18 schools, for example, the CO2 content was found to be almost always low, which indicates an active ventilation policy, presumably under the influence of the research that was conducted there! And it is at odds with other findings elsewhere.

Read full article: Another substandard Dutch study on aerosols

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Over two years ago I wrote an article titled “the aerosol deniers”. This included how people in the Netherlands denied that the spread of the virus through the air played an important role in the spread of Covid-19. While worldwide there is almost a consensus about the dominant role that aerosols play in the transmission of the virus, the Netherlands seems to be becoming something like the small village of Asterix and Obelix, which is the only one still able to withstand a force majeure.

Would it then be the case that the aerosols avoid the Netherlands because, just like the passengers at Schiphol, they have to wait a very long time before they can take to the air? Or is it still the unwillingness in the Netherlands to relinquish the positions from the spring of 2020.

RIVM literature studies

It started this week when I received an internal email from the RIVM from September 2020 from a WOB request. It was written by two persons who apparently had the task at RIVM to update the literature on aerogenic transmission. The e-mail shows that they do not have time for this because of the many parliamentary questions. But at the bottom of that email is a spicy sentence. They could call in an employee of the Z&O department (Zoonoses and environmental microbiology), but the problem was “that she conducts research into aerosols and mainly sends literature that shows that aerosols are important in the distribution”.

So that employee disqualifies herself by finding and distributing literature about the importance of aerosols in the distribution. Now this is exactly in line with the information I received from various sides from behind the scenes in the summer of 2020 that even if studies in the Netherlands showed hard evidence of the great importance of the aerosol dispersion that these studies should be kept under wraps. held.

And this “tradition” is maintained in the Netherlands. We saw several blatant examples of this in the past week.

A literature study was published by the RIVM on 22 September. It was about the effect of mobile air purifiers on transmission. The conclusion of that literature study is that too few studies have been found that indicate that mobile air purifiers have a positive effect on preventing the spread of Covid-19 or other viruses. Reference is also made to a literature study conducted by TNO, among others by researcher R. Traversi, whom I met during the round table discussion at the House of Representatives in mid-May and who also said that air purification would have little or no effect on the possible spread of the virus. I could hardly believe that in 2022 a researcher would still say that.

I have come across a number of studies myself, which show that good air purifiers with a good set-up can play an additional role on top of good ventilation. This study is published on the site of CDC (the American RIVM). Exposure to aerosols is reduced by approximately two thirds by an air filter installation (HEPA). And in the literature review of this study there are several others with more or less comparable results.

And this study also shows that the use of good air purifiers clearly reduces the spread of the virus via aerosols. And this 2020 classroom study also shows what the effect of the air filtering was in classrooms. The conclusion of that study is that spending two hours in a classroom with closed windows and a highly contagious person reduces inhaled doses by a factor of 6.

It is simply unwilling if you conclude in a literature study anno 2022 by the RIVM that there is too little evidence that mobile air filters work and more study is needed. (Probably the employee of the Z&O department from the email of the WOB request is not involved in this study or she has since left the RIVM disillusioned).

Research in Dutch schools

This week, the Minister of Education announced new measures to promote good ventilation in schools. A CO2 meter is mandatory.

I’ve been wondering for a long time now where the results of that study that apparently was held in Staphorst into the use of air filters from November 2021. Eindhoven University of Technology is said to have conducted research there. It can be concluded from the newspapers that the effect of the approach was very positive in Staphorst in the last two months of 2021. But during the Omikron period, classes had to be sent home, because three or more students had become infected.

Both as a researcher and as a father of a student who goes to secondary school, I find it remarkable how certain people apparently know when infections of students in schools that this happened at school. Of the approximately 15 infections that my daughter was aware of (or that concerned her), at least 10 were clear that they had not taken place at school! Pupils meet each other (and young people from other schools) not only at school! But also in other places, where conditions can be worse than at school.

Perhaps that is the reason that the study on the approach in Staphorst did not materialize or is not forthcoming.

But it only got really spicy that shortly after the minister’s announcement, news came about a Dutch study that was placed as a preprint in The Lancet. It concerned the research at 18 secondary schools between October 2020 and June 2021. If you read the summary that Maarten Keulemans wrote for de Volkskrant, you can see (once again) how eager he is to draw certain conclusions, while the study is more cautious in that regard, plus a still very big problem. This is what it says above his article:

The coronavirus does not spread so much through the air in secondary schools, but mainly through close, direct contact between students. A search of dozens of classrooms found exactly zero floating virus particles in the air, while there were many infections.

I looked at that study and immediately noticed the problems surrounding the measurement of the CO2 level. It was done twice during the study period in three classrooms per school. The CO2 value had only slightly exceeded the important limit of 800 PPM. Now I have given a CO2 meter in my daughter’s backpack to primary school a number of times and I noticed that the values ​​regularly shot far above 1000 PPM (sometimes even above 1500). Especially at the end of a class, when the teacher hadn’t opened the windows.

That is also what the clinical epidemiologist Deepti Gurdasani notes on the basis of that study and she has much more to criticize about that study, which she calls substandard. Her comments are in a series of tweets. This is the PDF with these tweets in it.

Here are some of her criticisms:

  • The CO2 level in the classrooms was only slightly above 800 and shows that for some reason (perhaps because the study was in progress) the ventilation in those schools was in good order. The researchers also mention this as an important limitation, but you will not find this in the publicity about the study.
  • Where the values ​​were above 800 PPM, a relationship can be seen between that high value and the increase in infections. But because the numbers are small, this is not significant.
  • There have been few measurements of the CO2 values ​​per school/classroom.
  • An important part of the study concerned the period when the classes were occupied with half or fewer students.

I state her closing remarks in full below. And that includes exactly my criticism of the study:

“We know that airborne dispersal is common in schools and other environments because we have *many* studies of superspreading in different scenarios – crowded indoor environments showing long-range outbreaks and rapidly expanding outbreaks in high-volume schools.

So you can look directly at the epidemiological evidence that clearly points to airborne transmission. Contrary to what that study says, this is not up for debate. And the epidemiological evidence trumps the inability to find the virus in the air, which is already hard to detect!

So we can’t roll back everything we’ve learned about airborne transmission over the past 2.5 years based on this!!!! Unfortunately, this study shows us nothing, except that substandard research should not be over-interpreted…
Again, many of us would spend a lot less time “debunking” these claims if “experts” didn’t make them — based on poor research. At the very least, read the study before making any claims!
And against the “I’m just sharing it without making any claims” as you cite the study on “close contact” as the primary mode of transmission – u are fully complicit in providing misleading information – because you cannot actually deduce this from the study!


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