The number of US adults who have contracted the novel coronavirus could be twice the number reflected in the official case count, according to a study published Tuesday in the medical journal JAMA.
Because many people who become infected with Covid-19 do not experience symptoms, researchers at the Clinical Reference Laboratory designed a large-scale study to test for the prevalence of SARS-CoV-2 antibodies in otherwise healthy US adults. SARS-CoV-2 is the virus that causes Covid-19.
The researchers enrolled 61,910 self-reported "well" participants. They tested their blood for antibodies to fight SARS-CoV-2, and found that 4,094 – or 6.6% – of them were positive, despite never reporting that they experienced symptoms.
The scientists used that information to estimate that 15.9 million asymptomatic or undiagnosed SARS-CoV-2 infections had occurred in the US as of September 30, 2020.
By contrast, the total number of confirmed positive cases was just over 7.2 million at the end of September, according to data compiled by Johns Hopkins University.
The researchers said the results of their study validate the need for ongoing population-wide surveillance testing for Covid-19.