Initial COVID-19 infection stats much higher than reported, researchers say

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Many epidemiologists believe that the initial novel coronavirus (COVID-19 infection) rate was undercounted due to testing issues, asymptomatic and alternatively symptomatic individuals, and a failure to identify early cases, according to new research by Pennsylvania State University published in the journal Science Translational Medicine.

In the paper, researchers estimated the detection rate of symptomatic COVID-19 cases using the U.S. Centers for Disease Control and Prevention's influenza-like illnesses (ILI) surveillance data over a three-week period in March 2020.

The researchers found that the excess ILI showed a nearly perfect correlation with the spread of COVID-19 around the country. The size of the observed surge of excess ILI corresponds to more than 8.7 million new cases during the last three weeks of March, compared to the roughly 100,000 cases that were officially reported during the same time.

The researchers also used this process to estimate 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. Their estimates showed rates much higher than initially reported but closer to those found once states began completing antibody testing.

In New York, for example, the researchers' model suggested that at least 9 percent of the state's entire population was infected by the end of March. After the state conducted antibody testing on 3,000 residents, they found a 13.9 percent infection rate, 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, which led to lower transmission rates.

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

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