Risk levels inaccurate due to undercounting in data sources vs wastewater data?

[sameerjain0123]

Summary

• 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
• 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?

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

[justinhaaheim]

@sameerjain0123 I'm not really sure how to interpret this wastewater data here. The increase that you're talking about from 2/9/22 to 2/15/22 goes back down after that. Possibly noise?

The microcovid model accounts for underreporting in general, but I don't know if it would account for a change in the underreporting factor due to a shift from people getting PCR tests to people using at-home antigen tests. It's not clear to me that the data you're sharing actually shows a statistically significant discrepancy here between JHU data and wastewater data given the possible noise/imprecision of the wastewater data, but I'm not an expert on the data side and will defer to others on that point.