We left at least 4 people behind in Carrion los Condes, too sick to walk. My partner walked but slowly, not arriving at the first albergue until 2:30. I started throwing up shortly after. These and other tales of woe from 3 different albergues.
No one knows for sure what the issue was but I would recommend caution drinking the municipal water.
I commented on a similar report in 2019, chiming in with my experience of Carrión de los Condes in August 2018 while staying at albergue Espiritú Santo, where two dorms had been quarantined off limits on arrival. I also met others during the following days who had similar symptoms while in Carrión de los Condes, although mainly from the albergue Santa Maria.
I seem to remember being shot down in flames for my opinions at the time, which I took as being good advice after all things considered. However, it would be helpful if there were some kind of register of such incidents, as maybe the pattern and location information would give insight into other possible explanations. Other than that, we are back to making cursory conclusions, just as I did, that may or may not have anything to do with it.
I guess it goes without saying, that lots of people grouped together in the same dormitory and/or sharing the same toilet facilities, is a situation where transmission of a virus, like Norovirus, could take place very easily. But there are many places on the Camino where people group together like this, so it does still beg the question about this reference to Carrión de los Condes and the possible link to people having stayed in Hontanas previously (as was my case).
The comments about water testing and water treatment are often cited as defense that it would be unlikely to be the source of contamination. However, along the way to Carrión de los Condes there are several water fountains that are marked as "no potable", so shouldn't be used as drinking water. Despite this notice, I've seen people using them to cool themselves down by putting their head under the fountains etc.
Getting a stomach virus of some kind can affect us anywhere I guess. I live in Madrid, and it's not uncommon to hear of these things from time to time. I had it myself in 2020 and the doctors suggested the most likely cause was food poisoning - but they don't test for it. So even medical professionals can resort to making assumptioms about causes, just as Joe Public does. I was prescribed antibiotics which immediately took affect in relieving the worse symptoms.
The comments about the pandemic somehow having the power to remove, or reduce, such supposed sources of contamination doesn't make sense to me - although extra hygiene measures (when maintained) should reduce risk of cross-infection at least. The only common denominator is volume of people in shared spaces - whether they be dorms in albergues or using the same limited number of restaurants and bars in a few towns where large numbers of pilgrims often stop at the end of a stage. Obviously, the "bug" needs to be "picked up" somewhere or from something or somebody - but we probably will never get to know that without a more rigorous approach to investigation of the causes. Then the "bug" needs to be transmitted to another person - hence the common denominator of numerous groups of pilgrims in shared facilities, in the same small town or at same restaurants; people that are in transit moving from town to town, village to village, albergue to albergue and also passing through various common "watering holes" and pilgrim pitstops. If I were a virus, I'd be rubbing my grubby little hands with glee....
At the risk of being shot down in flames again, I decided to chime in to this post, if nothing else to share my experience that relates to the OP.