Even in normal times, there was always tongue-in-cheek the concept of the "Kongressseuche" (congress plague), because many people got (mildly) ill with a cold or the flu. :)
The 2019 Congress plague was highly likely to have been covid in some cases, a number of attendees were quite ill after the event with respiratory symptoms. Given that covid had been circulating in Europe since at least November 2019, its not implausible.
Other years there were colds... The usual... But the 2019 edition was real nasty.
I didn't notice anything worse during 2019 than during previous years. There were fewer calls to sanitation, if anything, or perhaps the calls didn't stand out to me anymore. Either way, while you're probably right that the earliest cases of covid were probably already there, it's not as though "the congress flu" (never heard anyone call it 'plague', either) was because of covid, or because of covid even just that year.
I vaguely remember reading about the first handful of reported infections here on HN at the very end of 2019, somewhere around NYE. It was a very strange feeling to start the year with.
> "the congress flu" (never heard anyone call it 'plague', either)
I think the "Seuche" in Congress-Seuche falls somewhere in between. I can attest that at least Congress-Seuche has been in use in the past, somewhat analogous to the annual "Wiesnseuche" flu wave in Munich during and after the Oktoberfest.
Last time congress happened, I didn't speak German at all. I just meant the translation; that I've only ever heard it called flu (from what I remember). Things being lost in translation isn't new though, so of course I trust that the German word can mean that :)
The annual post congress malaise goes by many names. Conflu, CCCbola, Congress Plague, Congress Colds, "I didn't drink that much tschunk why do I feel shit a week later", etc ;)
