The Centers for Disease Control and Prevention issued new guidelines Thursday aimed at better identifying those who could be at greater risk of having a severe case of the COVID-19 virus.

The new guidelines stress that along with older people who have underlying health issues, those who are obese, are pregnant, have sickle cell disease or have asthma are at a greater risk of suffering from a severe case of the novel coronavirus.

“Understanding who is most at risk for severe illness helps people make the best decisions for themselves, their families and their communities,” CDC Director Dr. Robert Redfield said. “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.”

The updated guidance was based in part on the Center's Morbidity and Mortality Weekly Report.

In addition to issuing a warning about conditions that can lead to more serious disease, the report said that testing has led health officials to estimate that about 20 million Americans, or around 6% of the country’s population, has contracted COVID-19. However, Redfield said he believes that number could be far larger.

On a conference call with reporters after the new guidance was released, Redfield said, based on antibody testing, that at least 24 million Americans have likely been infected so far.

Redfield also told reporters that younger people are a big part of the transmission numbers.

“Young people, many newly mobile after months of lockdowns, have been getting tested more often in recent weeks and driving the surge in cases in the South and West,” he said.

Included in the new guidance are sharper definitions for categories of the population that the agency had previously pointed out could be at greater risk for infection.

While older adults and those with underlying medical conditions remain at increased risk for severe illness under the guidelines, the CDC now warns “that among adults, risk increases steadily as you age, and it’s not just those over the age of 65 who are at increased risk for severe illness.”

Eight out of 10 COVID-19 deaths reported in the United States have been in those 65 years old and older. The report also points out that the “risk in older adults is also in part related to the increased likelihood that older adults also have underlying medical conditions.”

The CDC also updated the list of those underlying medical conditions that tend to increase risk of severe illness. Those conditions include:

• Chronic kidney disease

• COPD (chronic obstructive pulmonary disease)

• Obesity (BMI of 30 or higher)

• Immunocompromised state (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

According to the CDC statement, an estimated 60% of American adults have at least one chronic medical condition, with obesity being one of the most common.

The CDC also announced on Thursday that other conditions may increase a person’s risk of having a more severe form of the virus. Those conditions include:

• Pregnancy – "Pregnant women were significantly more likely to be hospitalized, admitted to the intensive care unit, and receive mechanical ventilation than nonpregnant women; however, pregnant women were not at greater risk for death from COVID-19," the statement said

• Dementia

• Cerebrovascular disease – such as stroke

• Asthma

• High blood pressure