CDC director: There are likely about 10 cases of COVID-19 for every diagnosed case

While there is great variability nationwide, it appears between about 5% to 8% of the American public has been infected with the virus at this point, Centers for Disease Control and Prevention Director Robert Redfield, M.D., said. (

For every documented case of COVID-19 in the U.S., there are likely 10 more people who have been infected, the head of the Centers for Disease Control and Prevention (CDC) said Thursday. 

That's according to CDC serological data that have been collected so far and are still begin refined, CDC Director Robert Redfield, M.D., said in a call with reporters. 

A headshot of Robert Redfield
Robert Redfield, M.D. (CDC)

"At the beginning, we were seeing diagnosed cases of individuals who presented in hospitals and emergency rooms and at nursing homes. We were selecting for symptomatic or higher risk groups … there wasn't a lot of testing of younger, asymptomatic individuals," Redfield said. "I think it's important for us to realize that we probably recognized about 10% of the outbreak by the methods that were used to diagnose between March, April and May. We're continuing to try to enhance surveillance systems for individuals that are asymptomatic, being able to the testing of asymptomatic infection more in real time."

While there is great variability nationwide, it appears between about 5% to 8% of the American public has been infected with the virus at this point, Redfield said.

That means many individuals across the nation are still susceptible to the virus, and some states' populations may be more susceptible than others at this point to virus because they have a lower antibody prevalence. 

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During the call, the CDC also announced it was clarifying information about which groups were most at risk for complications from COVID-19 based on emerging evidence. Older individuals are still considered at greatest risk, most likely because they are at greatest risk for having multiple underlying conditions, officials say.

According to the CDC, the underlying conditions with the strongest evidence of higher risk include cardiovascular disease, chronic kidney disease, chronic obstructive pulmonary disease, obesity, immunosuppressing conditions or treatments, sickle cell disease, a history of organ transplant and Type 2 diabetes.

They also clarified the underlying conditions that might increase the risk of severe illness such as chronic lung diseases including severe asthma or cystic fibrosis, high blood pressure, a weakened immune system such as after a blood or bone marrow transplant, immune deficiency or neurological conditions such as dementia or a history of stroke, liver disease and pregnancy.

Officials said analysis of surveillance data showed pregnant women with COVID-19 were more likely to be admitted to the ICU and receive mechanical ventilation than non-pregnant women. However, they said, the available data do not appear to show pregnant women are at higher risk of death from COVID-19.

"We are collecting additional information and are working to find out if COVID-19 is associated with pregnancy complications," said Jay Butler, M.D., the CDC's incident manager, said on the call.