“Our best estimate right now is that for every case that was reported, there actually were 10 other infections,” Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, said during a conference call Thursday. Redfield is pictured during a hearing of the House Committee on Energy and Commerce on Tuesday.

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“Our best estimate right now is that for every case that was reported, there actually were 10 other infections,” Dr. Robert Redfield, director of the Centers for Disease Control and Prevention, said during a conference call Thursday. Redfield is pictured during a hearing of the House Committee on Energy and Commerce on Tuesday.

Kevin Dietsch-Pool/Getty Images

Millions of Americans have probably had the virus without knowing it.

That’s the conclusion of officials at the Centers of Disease Control and many other experts. “Our best estimate right now is that for every case that was reported, there actually were 10 other infections,” Dr. Robert Redfield, the director of the CDC, said during a call with reporters Thursday.

Redfield estimates that between 5% to 8% of the U.S. population has been exposed. He points to results from community-wide antibody tests and other surveillance measures that point to this range. But he emphasizes, that leaves more than 90% of Americans who’ve yet to be exposed and remain susceptible.

To date, 2.3 million Americans have confirmed coronavirus cases but by these estimates, the real number could be at least 20 million.

These estimates validate what many public health researchers suspected: that we’ve failed to capture with testing much of the spread of our virus within some communities.

“In the beginning, there wasn’t a lot of testing that was done of younger, asymptomatic individuals,” Redfield said. “So I think it’s important for us to realize that we probably recognized about 10 percent of the outbreak by the methods that we use to diagnosis between the March, April and May.”

And certain people are more susceptible to very serious illness from COVID-19. The CDC points to consistent evidence from studies that a range of conditions are linked to more severe illness from COVID-19. They include chronic kidney disease, COPD (chronic obstructive pulmonary disease), Type-2 diabetes, obesity (defined as BMI of 30 or higher), chronic heart disease, people who are immunocompromised and those with sickle cell disease.

Age also plays a role in the risk of serious illness, with most deaths from COVID-19 documented in people 65 and older. And the risk for serious illness or death increases the older you are.

“While we are all at risk for COVID-19, we need to be aware of who is susceptible to severe complications so that we take appropriate measures to protect their health and well-being,” Redfield said. The more risk factors people have, the higher their risk of serious illness or death. In fact, an analysis in the MMWR published last week found that people with chronic conditions were 12 times more likely to die from the virus, compared with those who didn’t have underlying conditions.

Given that about 60% of American adults have one or more chronic medical conditions, it’s clear that many are at elevated risk of severe illness from COVID-19. Lifestyle-related diseases including Type-2 diabetes and obesity are among the most common conditions in the U.S. These conditions can increase inflammation and tamp down the immune system.

In addition, the CDC published a new analysis Thursday pointing to increased risks for pregnant women from COVID-19. Although pregnant women are not at greater risk of death from the virus, the study finds they are more likely to be hospitalized and more likely to be admitted to the ICU. They’re also more likely to require intubation for breathing support compared to women who are not pregnant.

Given the risks, Redfield urged Americans to continue to take precautions. “This is still serious. It’s significant,” he emphasized. Case counts are on the rise in many Sun Belt states, and the virus continues to circulate widely.

“The most powerful tool that we have is social distancing,” Redfield said. He also pointed to the importance of face coverings and good hand hygiene. “It’s really important. [These are] really powerful tools. And as we go into the fall, in the winter, these are going to be really, really important defense mechanisms.”