Unmasking the Actual COVID-19 Case Count

Abstract

This report presents a novel approach to estimate the total number of COVID-19 cases in the United States, including undocumented infections, by combining the Centers for Disease Control and Prevention's influenza-like illness surveillance data with aggregated prescription data. We estimated that the cumulative number of COVID-19 cases in the United States by 4 April 2020 was > 2.5 million.

Keywords: CDC’s influenza-like illness report; aggregated prescription data; influenza-like illness; total case count; undocumented infection.

Figure 1.

The estimated influenza level before and after mid-February 2020. Prior to mid-February 2020, our estimated influenza level (blue line) closely matches the Centers for Disease Control and Prevention (CDC)–reported influenza-like illness (ILI) level (black line), but significant gaps between the 2 levels (red and black lines) emerge after mid-February, which can be attributed to COVID-19. To estimate the COVID-19 weekly case counts shown in the figure, we used the ILI total counts reported in ILINet, the reported 8.5% sampling rate of ILINet, and the reported 50% ± 8% rate of persons with symptomatic ILI seeking medical care for their illness. For the reported rates, see https://www.cdc.gov/flu/about/burden/preliminary-in-season-estimates.htm and https://www.cdc.gov/flu/about/burden/how-cdc-estimates.htm.