Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, speaks about the coronavirus in the James Brady Press Briefing Room of the White House in Washington on April 22, 2020.
Alex Brandon—AP
June 25, 2020 3:17 PM EDT

In a press briefing on June 25, Dr. Robert Redfield, director of the U.S. Centers for Disease Control and Prevention (CDC), said that the current official count of COVID-19 cases in the U.S. may actually be a drastic underestimate.

Redfield said the new, much-higher estimate, is based on growing data from antibody testing, which picks up the presence of immune cells that react to SARS-CoV-2, the virus that causes COVID-19. People will test positive for antibodies to the virus if they have been infected—whether or not they ever got sick or even developed symptoms.

Previously, testing was focused only on those with symptoms. But because so many who become infected with SARS-CoV-2 could either have mild disease or not know they were infected at all, Redfield said, current information on the burden of cases is an underestimate. “The traditional approach of looking for symptomatic illness, and diagnoses obviously under estimated the total number of infections,” Redfield said. “Now that serology tests are available, which test for antibodies, the estimates we have right now show about 10 times more people have antibodies in the jurisdictions tested than had documented infections.”

That fact may also be contributing to the recent downward trend in the average age of people being diagnosed, since, as Redfield noted, those people were likely not being diagnosed in the past—younger people are less likely to experience the severe symptoms that bring them to the attention of the health care system, where the early cases were documented. Now that testing is more widely available in the community, it’s becoming clear that more people are currently infected or have recovered from COVID-19 than was previously believed.

On the press call, the CDC also announced changes to its definitions of people at high risk of COVID-19; it now includes those with asthma, dementia and a history of stroke, as well as people who are pregnant. The absolute risk of infection for these groups is still low, but compared to those without these conditions, the risk is worth noting. Based on new data, the CDC also updated its list of underlying medical conditions that could make people more vulnerable to COVID-19 to now include obesity and type 2 diabetes, conditions that are both common in the U.S. population, including among younger people.

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