Thoughts on seroprevalence in NYC. I'm not at all surprised by an estimate of 21% seropositive in NYC as discussed by @NYGovCuomo today ( https://twitter.com/NYGovCuomo/status/1253353516803993600). 1/6

I had previously been estimating a case-to-infection reporting ratio of 10-20X ( https://twitter.com/trvrb/status/1249414308355649536). I can't figure out when this 21% seropositive estimate refers to, but we can do some extremely rough calculations assuming 21% today. 2/6

As of today, NYC has had 145k confirmed cases reported ( https://www.nytimes.com/interactive/2020/us/coronavirus-us-cases.html). Assuming seroprevalence of 21% gives 1.7M infections in a city population of 8.4M. Dividing 1.7M by 145k gives a reporting ratio of ~12X. 3/6

This reporting ratio of 12X seems entirely within the realm of expectation. If we then take deaths as of today as 17,200 based on excess deaths ( https://www.nytimes.com/interactive/2020/04/21/world/coronavirus-missing-deaths.html), we'd get an infection-to-fatality ratio of ~1%. 4/6

This estimate deserves better statistics as there are active infections among the 1.7M that will resolve to deaths in the coming weeks (increasing the numerator) and the true seroprevalence may be greater today than when the study was conducted (increasing the denominator). 5/6

Keep in mind that this infection-to-fatality ratio is heavily dependent on population demographics as well as health system capacity. IFR of ~1% (or more) in NYC may differ from IFR in other locations. 6/6