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Large numbers of COVID-19 cases have been undetected and unreported, which has resulted in severe undercounting of the total number of people who have been infected during the pandemic, according to a new study published Monday in the journal PLoS One.
In the U.S., the number of COVID-19 cases is likely 3 times that of reported cases. According to the study, more than 71 million Americans have contracted the virus during the pandemic, and 7 million were infected or potentially contagious last week.
Public health officials rely on case counts to guide decisions, so the undercounting should be considered while trying to end the pandemic.
"The estimates of actual infections reveal for the first time the true severity of COVID-19 across the U.S. and in countries worldwide," Jungsik Noh, a bioinformatics professor at the University of Texas Southwestern Medical Center, said in a statement.
Noh and colleague Gaudenz Danuser created a computational model that uses machine-learning strategies to estimate the actual number of daily cases in the U.S. and the 50 most-infected countries.
The model pulls data from the Johns Hopkins University database and the COVID Tracking Project, as well as large-scale surveys conducted by the CDC and several states. The algorithm uses the number of reported deaths, which is thought to be more accurate than the number of lab-confirmed cases, as the basis for calculations.
In 25 of the 50 countries, the "actual" cumulative cases were estimated to be 5 to 20 times greater than the confirmed cases. In the U.S., Belgium, and Brazil, about 10% of the population has contracted the coronavirus, according to the model. At the beginning of February, about 11% of the population in Pennsylvania had current infections, which was the highest rate of any state. About 0.15% of residents in Minnesota had infections, and about 2.5% of residents in New York and Texas had infections.
"Knowing the true severity in different regions will help us effectively fight against the virus spreading," Noh said. "The currently infected population is the cause of future infections and deaths. Its actual size in a region is a crucial variable required when determining the severity of COVID-19 and building strategies against regional outbreaks."
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