COVID-19 clusters in Belgium

Recently (I’m writing this on October 20), the (new) Belgian government decided to apply more stringent prophylaxis measures to contain COVID-19. One of the controversial measure is to close bars and restaurants for a month.

Unfortunately, in a way, at approximately the same time, AVIQ released its latest poll on COVID-19 clusters in Wallonia (AVIQ is the Walloon agency for well-being, health, handicap and family). I wrote it was unfortunate because I read and heard several people who criticized the closing of bars and restaurants by citing this poll. But this poll cannot answer in favor or against this closure; it doesn’t look at that …

Here are the results:

From the meager press release, here is what we can reconstruct … AVIQ looked at the 5,043 COVID-19 clusters in Wallonia so far and went to interview one or several patients from these clusters (AVIQ defines a cluster as a place where there are 2 or more confirmed COVID-19 cases). The question was, more or less, where did you go before getting COVID-19? (in French: “collectivités que les personnes covid-19 positives ont déclaré avoir fréquentées“).

From there, nearly 84% of clusters were families, far ahead from schools (4%), companies/bars/restaurants (3%), and other places (note schools are still open in Belgium, except universities starting today).

First, bars and restaurants are amalgamated with companies (where home working was encouraged). One cannot easily disentangle them, unfortunately. Then all places are linked and the virus didn’t suddenly appear in the family – but one is more inclined to remember it’s in the family because it is close to dear people (spouse, children, parents, …). Also, there is the potential recollection bias (a classical limitation of interviews), interviewees willing to please the interviewer or simply not willing to disclose behaviors that may be frowned upon. A recent example of this was when the previous Belgian Prime Minister announced she was positive:

This tweet was quickly put in perspective with a plenary meeting of Mrs Wilmès party where the recommended precautions were not all followed:

Well, back to our clusters … My last points for this AVIQ poll is that unfortunately there is no more details than this. We don’t know much about the methodology, it was minimally put in context and there was little caution against wild interpretations (just a “[Ces données] restent toutefois parcellaires compte tenu de ce qu’elles sont déclaratives et tributaires des délais de testing“).

On the other side of Belgium, Zorg en Gezondheid (~AVIQ in the Flemish Region) did a similar poll but gave a bit more details about how they did it and provided more explanations in the results. For instance, they started by asking the index patient where he/she thinks he/she was contaminated: in the chart below, most patients didn’t know (“onbekend” – at least it was an option) but family (“gezin“) and workplace (“werk“) are respectively second and third in the places where they think they most likely got infected (but quite behind “unknown”).

What is interesting is that Zorg en Gezondheid then asked in which social places were these patients before self-isolating. And then we see (below) than most mention bars (“cafés“), restaurants, sports and then only the rather vague “public activities”. It is striking to note that none of these activities are related to school (maybe they only interviewed adults?).

And again, as it was mentioned elsewhere, these are interesting results but it doesn’t show the contagiousness or risk of contamination of these places.

For that, you’ll need serious tracing studies following knows outbreaks. But that’s another story …

To be continued …

As usual, you’ll find other graphs on my page about COVID-19 in Belgium (and figures above are updated with new data as they appear) and the data, code and figures are on Github (including the AVIQ one in this post).

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