The true number of coronavirus cases in the U.S. may be eight times higher than previously reported, according to a new estimate by the U.S. Centers for Disease Control and Prevention (CDC). 

Between February 27 and September 30, the tally of COVID-19 infections may have reached nearly 53 million, about eight times of the reported number of 6.8 million, CDC researchers wrote in a paper published November 25 in the journal Clinical Infectious Diseases.

They said it's because of the incomplete reporting of cases, the neglect of asymptomatic or mildly ill individuals who never got tested, as well as those who got false-negative test results.  

That means people may carry and spread the coronavirus while showing only minor symptoms or even no symptoms at all, they warned.  

The report comes as the U.S. hit another grim milestone, with the number of reported COVID-19 cases surpassing 13 million. So far, the virus has claimed 266,000 American lives.