The real number of U.S. coronavirus cases could be as high as 23 million — 10 times the 2.3 million currently confirmed cases — the Centers for Disease Control and Prevention told reporters yesterday, Axios’ Marisa Fernandez reports.

Between the lines: The new estimate is based on antibody testing, which indicates whether someone has previously been infected by the virus regardless of whether they had symptoms.

• “This virus causes so much asymptomatic infection. The traditional approach of looking for symptomatic illness and diagnosing it obviously underestimates the total amount of infections,” CDC director Robert Redfield said.

The agency also expanded its warnings of which demographic groups are at risk, which now include younger people who are obese and who have underlying health problems.

• The shift reflects what states and hospitals have been seeing since the pandemic began, which is that young people can get seriously ill from COVID-19.

The new guidance also categorizes medical conditions that can affect the severity of illness:

• Conditions that increase risk: Chronic kidney disease; chronic obstructive pulmonary disease; obesity; weakened immune system from solid organ transplant; serious heart conditions, such as heart failure, coronary artery disease or cardiomyopathies; sickle cell disease; Type 2 diabetes.
• Conditions that may increase risk: Chronic lung diseases, including moderate to severe asthma and cystic fibrosis; high blood pressure; a weakened immune system; neurologic conditions, such as dementia or history of stroke; liver disease; pregnancy.