The Nation’s Reported Covid-19 ‘Cases’ Are a Mix of Bad Math and Bad Reporting

If we want to use testing to effectively control this pandemic, this is what we need (now)

Photo: Mufid Majnun on Unsplash

The U.S. Centers for Disease Control and Prevention (CDC) and many media outlets report the daily number of “new cases of Covid-19 infection in the United States.” They also regularly report infection rates—that is, the proportion of those tested who are positive. Such reporting occurs in other nations as well. But these statistics are misleading.

Testing for Covid-19 infection in the population serves three critical purposes in pandemic control:

1. With the antigen test for Covid-19, the purpose is finding people who are currently infected and, if needed, recommending treatment or quarantine.
2. Contact tracing, and then, if needed, recommending quarantine or treatment.
3. With the antibody serology test, the goal is assessing the spread and monitoring trends of recent or past infection in the overall population to better understand the pandemic, ultimately to improve disease control.

Covid-19 testing numbers reported daily by the CDC and the media may be moderately effective for the first purpose, but they are not optimal for any of these purposes. Moreover, this number is not, as typically reported, “Covid-19 in the United States.” While reported numbers of Covid-19 deaths are a reasonable approximation of death counts in the population, the number of reported Covid-19 cases represents only the number of people who happen to get tested where testing happens to be available and that have shown to be positive. These “cases” are an unknown mixture of people who are asymptomatic, symptomatic, and those with Covid-19 who have been tested — again, where testing happens to be available. Estimating the number of cases in the population requires random, representative population sample testing. National counts and rates have been estimated to be more than 10 times what is reported in the media from available testing. Estimates of mortality rates associated with Covid-19 infection based on reported infection will be correspondingly exaggerated.