The true number of Americans who've been infected with COVID-19 may top 20 million, according to new estimates from the Centers for Disease Control and Prevention.
"Our best estimate right now is that for every case that's reported, there actually are 10 other infections," Dr. Robert Redfield, director of the CDC, said on a call with reporters Thursday.
The assessment comes from looking at blood samples across the country for the presence of antibodies to the virus. For every confirmed case of COVID-19, 10 more people had antibodies, Redfield said, referring to proteins in the blood that indicate whether a person's immune system has previously fought off the coronavirus.
Those samples aren't just from people who have had antibody testing. They also come from testing performed on donated blood at blood banks or from other laboratory testing of blood.
Currently, there are 2.3 million COVID-19 cases reported in the U.S. The CDC's new estimate pushes the actual number of coronavirus cases up to at least 23 million.
"This virus causes so much asymptomatic infection," Redfield said. "The traditional approach of looking for symptomatic illness and diagnosing it obviously underestimates the total amount of infections."
The estimation comes amid rises in cases across the Southeast and Western U.S., particularly among younger adults in their 20s, 30s and 40s.
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Also Thursday, the CDC expanded its list of who is at greatest risk for COVID-19 complications, removing the age cutoff of 65.
"There's not an exact cutoff of age at which people should or should not be concerned," Dr. Jay Butler, head of the COVID-19 response at the CDC, said. Rather, a person's risk increases with age, but that doesn't preclude younger adults from complications.
Indeed, people of any age with certain underlying health conditions have a higher risk, though the likelihood of having these conditions increases with age. At risk are those with heart disease, chronic kidney disease, chronic obstructive pulmonary disease, obesity, type 2 diabetes, sickle cell disease and anyone with a compromised immune system.
CDC also clarified the list of other conditions that might increase a person’s risk of severe illness, including asthma, high blood pressure, neurologic conditions such as dementia, cerebrovascular disease such as stroke, and pregnancy.
Research published on Thursday from the CDC specifically addressed the risk in pregnant women. When compared to nonpregnant women with the virus, pregnant women with COVID-19 were more likely to be hospitalized, admitted to the intensive care unit and put on a ventilator.
Death rates between the two groups of women, however, were similar.
Redfield also urged Americans to be vigilant about behavior measures known to minimize spread of the coronavirus, particularly as the country heads into the July Fourth holiday.
The coronavirus spreads mainly from person to person through respiratory droplets from coughing, sneezing, talking and singing.
"The most powerful tool that we have is social distancing," he said. That means maintaining a physical distance of at least 6 feet in public, wearing face coverings and regular hand-washing.
"If you must go out into the community, being in contact with fewer people is better than many," Redfield added.