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You know me, I like to work through lists of possible explanations for stuff. We're seeing a huge surge in COVID wastewater signal in several places, are there are several possible (non-mutually-exclusive) explanations for it that are worth contemplating. 🧵
Why so much COVID in wastewater? Several non-mutually-exclusive possibilities: 1. More cases, 2. More virus per case in general, 3. More virus in the gut specifically, 4. Longer-lasting infections.
1. More COVID cases. The most obvious explanation, and the one that raises the most alarm, is that there are just a LOT of COVID infections right now. (And absent evidence that something has changed, this is the default).
2. Higher average viral load per infection overall, meaning that each person sheds more virus because each person has more virus in their body. (Again, this would require evidence to back it up, which we don't have currently.)
3. Higher viral load specifically in the digestive tract. Tropism of the virus (i.e., which tissues it infects) can shift, so it's possible that newer variants hang out in the gut more and thus are shed in greater amounts in wastewater. (Again, no evidence currently.)
4. Longer-lasting infections. If people are infected and shed virus for longer, there will be more overlap in shedding among cases, and thus more virus in wastewater overall even without a change in total number of cases. (You guess it, no evidence currently.)
Right now, the assumption remains that there is just a huge number of infections right now. But some of the other possible factor could be involved too, which is why we need to continue monitoring wastewater and studying evolving variant lineages.
It's worth noting whether other metrics (test positivity for non-wastewater, hospitalizations, etc.) are following the same pattern of increase right now. (Yes)
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