From this article:
The true number of Americans who’ve been infected with COVID-19 may top 20 million, according to new estimates from the Centers for Disease Control and Prevention.
“Our best estimate right now is that for every case that’s reported, there actually are 10 other infections,” CDC Director Dr. Robert Redfield said on a call with reporters Thursday.
The assessment comes from looking at blood samples across the country for the presence of antibodies to the virus. For every confirmed case of COVID-19, 10 more people had antibodies, Redfield said, referring to proteins in the blood that indicate whether a person’s immune system has previously fought off the coronavirus.
Those samples aren’t just from people who have had antibody testing. They also come from testing performed on donated blood at blood banks or from other laboratory testing of blood.
I’ve been estimating total infections using death counts. Based on published, well-designed antibody surveys, the US’s age-adjusted covid mortality rate is around 0.6 percent. On average, how many infections does it take to produce one death? 1/.006 = 167. Multiply the total number of covid deaths by 167 to estimate the total number of infections:
125 thousand deaths x 167 infections per death = 20.8 million covid infections