Initial COVID-19 infection rate may be 80 times higher than originally reported

Many epidemiologists believe that the initial infection rate with COVID-19 was not counted due to testing problems, asymptomatic and alternatively symptomatic individuals, and a failure to identify early cases.

Now, a new Penn State study estimates that the number of early cases of COVID-19 in the US USA It may have been over 80 times larger and doubled almost twice as fast as originally believed.

In an article published today (June 22) in the magazine Medicine Translational Medicine, the researchers estimated the detection rate of symptomatic cases of COVID-19 using surveillance data for influenza-like illness (ILI) from the Centers for Disease Control and Prevention over a three-week period in March 2020 .

“We analyzed ILI cases from each state to estimate the amount that could not be attributed to influenza and exceeded seasonal reference levels,” said Justin Silverman, assistant professor at the College of Information Science and Technology and the Department State Department of Medicine. “When you subtract this, you’re left with what we call excess ILI: cases that cannot be explained by either influenza or the typical seasonal variation of respiratory pathogens.”

The researchers found that excess ILI showed an almost perfect correlation with the spread of COVID-19 across the country.

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

Surprisingly, the size of the observed increase in excess ILI corresponds to more than 8.7 million new cases during the last three weeks of March, compared to the approximately 100,000 cases that were officially reported during the same time period.

“At first I couldn’t believe our estimates were correct,” said Silverman. “But we found that deaths in the US had doubled every three days and that our estimate of the infection rate was consistent with the doubling of three days since the first observed case was reported in the state of Washington on January 15. “

The researchers also used this process to estimate infection rates for each state, noting that states that show higher infection rates per capita also had higher per capita rates of excessive ILI increase. Their estimates showed rates much higher than those initially reported but closer to those found once states began completing antibody tests.

In New York, for example, the researchers’ model suggested that at least 9% of the state’s entire population was infected in late March. After the state conducted antibody tests on 3,000 residents, they found an infection rate of 13.9%, or 2.7 million New Yorkers.

Excess ILI appears to have peaked in mid-March, as the researchers suggest fewer patients with mild symptoms sought care and states implemented interventions that led to lower transmission rates. Almost half of the states of EE. USA They had orders to stay home before March 28.

The findings suggest an alternative way of thinking about the COVID-19 pandemic.

“Our results suggest that the overwhelming effects of COVID-19 may have less to do with the lethality of the virus and more to do with how quickly it initially spread through communities,” Silverman explained. “A lower mortality rate coupled with a higher prevalence of disease and a rapidly growing regional epidemic provides an alternative explanation for the large number of hospital deaths and overcrowding that we have seen in certain areas of the world.”