Story at a glance
- The report led by researchers from Penn State University analyzed surveillance data on influenza-like illnesses from the CDC that were never diagnosed as coronavirus, influenza or any other viruses.
- The researchers found a spike in influenza-like illnesses in March showed a nearly perfect correlation with the spread of coronavirus around the country.
- Researchers also estimated infection rates for each state, noting that states showing higher per capita rates of infection also had higher per capita rates of a surge in excess influenza-like illnesses.
A new study suggests the number of coronavirus cases in the U.S. in March could have been 80 times greater and doubled nearly twice as fast than originally reported, amounting to more than 8.7 million coronavirus cases that went undiagnosed.
The report, led by researchers from Penn State University (PSU), analyzed surveillance data on influenza-like illnesses (ILI) from the Centers for Disease Control and Prevention (CDC) xthat were never diagnosed as coronavirus, influenza or any other viruses over a three-week period in March, according to the study published in the journal Science Translational Medicine.
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“The findings support a scenario where more than 8.7 million new SARS-CoV-2 infections appeared in the U.S. during March and estimate that more than 80% of these cases remained unidentified as the outbreak rapidly spread,” Justin Silverman of Penn State, Alex Washburne of Montana State University and colleagues at Cornell University and elsewhere wrote, CNN reported.
Only about 100,000 coronavirus cases were reported during that period in March, as there was a shortage of testing kits at the time. More than 2.3 million cases have been reported in total in the U.S. with more than 120,000 deaths. Worldwide, more than 9.1 million cases have been confirmed.
"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 in a press release.
"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," Silverman added.
Silverman said researchers at first could not believe their estimates were correct, but realized that deaths across the U.S. had been doubling every three days and that the estimate of the infection rate was consistent with three-day doubling since the first observed case was reported on Jan. 15 in Washington state.
The researchers found a spike in ILI in March showed a nearly perfect correlation with the spread of coronavirus 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.
Researchers also estimated infection rates for each state, noting that states showing higher per capita rates of infection also had higher per capita rates of a surge in excess ILI.
"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," Silverman said.
"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."
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