Nearly 9 Million Americans With Coronavirus Went Undiagnosed in March, Study Suggests

by Ethen Kim Lieser

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New research from Penn State University is suggesting that the number of U.S. COVID-19 cases in March may have been 80 times greater than what was originally believed.

The findings, which were published in the journal Science Translational Medicine, have revealed that there were more than 8.7 million coronavirus cases that health officials and the public never knew existed.

Many epidemiologists believe that the initial COVID-19 infection rate was undercounted due to testing issues, asymptomatic spreaders and high false-negative rates.

“Our results suggest that the overwhelming effects of COVID-19 may have less to do with the virus’ lethality and more to do with how quickly it was able to spread through communities initially,” the study’s co-author Justin Silverman, an assistant professor at Penn State’s College of Information Sciences and Technology and Department of Medicine, said in a release.

“A lower fatality rate coupled with a higher prevalence of disease and rapid growth of regional epidemics provides an alternative explanation of the large number of deaths and overcrowding of hospitals we have seen in certain areas of the world.”

The study was able to estimate the detection rate of symptomatic COVID-19 cases using the Centers for Disease Control and Prevention’s influenza-like illnesses (ILI) surveillance data over a three-week period in March.

“We analyzed each state’s ILI cases to estimate the number that could not be attributed to influenza and were in excess of seasonal baseline levels,” Silverman said.

“When you subtract these out, you’re left with what we’re calling excess ILI—cases that can’t be explained by either influenza or the typical seasonal variation of respiratory pathogens.”

The researchers soon discovered that the excess ILI matched up nearly perfectly with the spread of COVID-19 around the country.

“This suggests that ILI data is capturing COVID cases, and there appears to be a much greater undiagnosed population than originally thought,” Silverman said.

In the last three weeks of March, only about 100,000 cases were officially reported in the U.S.

“At first I couldn’t believe our estimates were correct,” Silverman said. “But we realized that deaths across the U.S. had been doubling every three days and that our estimate of the infection rate was consistent with three-day doubling since the first observed case was reported in Washington state on Jan. 15.”

Ethen Kim Lieser is a Minneapolis-based Science and Tech Editor who has held posts at Google, The Korea Herald, Lincoln Journal Star, AsianWeek and Arirang TV. Follow or contact him on LinkedIn.