Summary
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As people are increasingly using at-home tests instead of PCR, I’m concerned that the data sources for microCOVID are underreporting risk. Trends in wastewater data substantiate this concern
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Am I missing anything, such that we think that microCOVID’s risk calculations are still sufficiently accurate to be useful? If not, any suggestions on how to adjust to account for this?
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(Obviously, this only matters if you think that getting COVID is a concern. I’m still digesting Zvi’s post on this vs. claims that Long COVID is much more likely than he suggests, but that’s a separate discussion, so let’s set it aside here.) Details(HT: My friend Alice) Because so many COVID cases aren’t officially recorded, I checked to see if microCOVID’s calculator factors in COVID levels in wastewater—wastewater is a more accurate way of measuring COVID levels. To do this, I did a site search of https://www.microcovid.org/ for wastewater and got no results. Then I checked the CovidActNow site, which you said that microCOVID sources from, and it doesn’t track wastewater, at least not in Alameda County. See https://covidactnow.org/us/california-ca/county/alameda_county/?s=30471905 . Because you said that microCOVID also sources from John Hopkins, I checked their COVID map here: https://coronavirus.jhu.edu/us-map --, from what I found, they don’t appear to track wastewater either. See https://bao.arcgis.com/covid-19/jhu/county/06001.html . Unfortunately, the COVID levels in Alameda County’s wastewater are going up, and those levels are now higher than they were on February 9. You can see this from the screenshot I took below from https://data.covid-web.org/ . (I used "log" for the Y axis scale, so you can clearly see how COVID levels in wastewater have recently been changing.)
The CovidActNow and the John Hopkins COVID map don’t reflect a recent rise in COVID levels to anything like the levels on February 9. So I don’t think those sites are accurately reflecting the recent increase in COVID levels. I’m guessing that more people are using home tests (which are now much more easily available and are reimbursable by insurance) instead of PCR tests. The New York Times Case Tracker explains the following about COVID cases that are included on their graphs:
Confirmed cases and deaths, which are widely considered to be an undercount of the true toll, are counts of individuals whose coronavirus infections were confirmed by a molecular laboratory test. This explanation is on the NYT’s case tracker page for Alameda County here: https://www.nytimes.com/interactive/2021/us/alameda-california-covid-cases.html . Given the increasing COVID levels in Alameda County wastewater, and given that microCOVID’s calculator doesn’t seem to factor in those increases, I think that microCOVID is underestimating the /COVID risk at events around Alameda County.
I don’t know the situation for California but my guess is that you’re right about your suspicion. I’ve been keeping an eye on London case numbers from reported tests and on numbers from the Zoe Covid study. Numbers from the latter started to rise to concerning levels well before positive tests started to rise. And now it’s the entire UK that’s under a surge of Omicron BA.2. I assume the same thing is playing out in other places, and for whatever reasons, be it testing or something else, the positive tests may lag behind other indicators. (The Zoe Covid study is based on regular self-reports on symptoms via an app.)