There has been a lot of excitement over wastewater testing for COVID. Even pundits who know no microbiology are excited about it! Wastewater testing is useful, but there are a couple of caveats. First, the way the CDC reports the data is essentially useless. The percent change over the last fifteen days doesn’t really help. Not only doesn’t it tell us the absolute level of COVID and thus can’t be compared to earlier periods, but it is extremely difficult to interpret. If we drop from a 455% increase to a 148% 15-day increase, we can’t really determine what that means. Some states are reporting the data using actual measurement values–of course, D.C. Water and DC Health aren’t (good job, Mayor Bowser!).
The second issue, and more serious, is that it’s clear policy makers won’t do anything with these data–they haven’t really done so to date, and there’s no reason to think they’ll start. Even with reporting of absolute levels, I wouldn’t know when to take additional precautions (though it might be useful for hospitals so they can prepare).
Speaking of hospitals, that brings us to the other data we need, which I’ve been calling for since 2020: the percentage of asymptomatic hospital patients who test positive for COVID. It’s not perfect, but it gives us a real-time indication of what the prevalence of COVID is in the community. If you need to know what the prevalence–which is to say, the risk–is, this would certainly provide what you need: is the prevalence ten percent, one percent, less than a tenth of a percent? That’s useful information for individuals, and since our ‘national’ policy is to leave it up to individuals to protect themselves, at the very least, give us the damn data to do so.
Wastewater is good, but we also (still) need the asymptomatic patient data too.