How many people have coronavirus but no symptoms? An alarming number, experts say

Asymptomatic infections among coronavirus patients may be higher than expected, experts say.

A study published in JAMA Network Open found that 42% of COVID-19 cases in a group of people in a hospital in Wuhan, China, were asymptomatic.

Of the 78 patients at Zhongnan Hospital of Wuhan University confirmed with COVID-19, 33 were asymptomatic and 45 were symptomatic. The patients were admitted from Dec. 24, 2019, to Feb. 24. The patients had a history of being exposed to the Hunan seafood market or they were in close contact with someone else diagnosed with COVID-19.

Symptoms, signs, chest computed tomography scans, treatment, laboratory values, and outcomes were measured.

In another study published in Thorax, more than 80% of people who tested positive for COVID-19 on a cruise ship didn’t show symptoms.

The ship, leaving from Argentina in March, was set to travel around the Antarctic Peninsula. Passengers were screened for coronavirus symptoms and eight days into the journey, one passenger developed a fever. The ship docked in Uruguay and eight people were evacuated.

Passengers were tested again and of the 217 people, 128 were positive for COVID-19, but only 24 showed symptoms before testing. Of the remaining 104 people, 81% of those who were confirmed to have COVID-19 didn’t experience symptoms, researchers said.

The Centers for Disease Control and Prevention also released a new guidance and said its “best estimate” for asymptomatic infections was 35% among COVID-19 cases.

CDC Director Robert Redfield previously said in an interview with NPR that “as many as 25%” of cases are asymptomatic.

“That may be as many as 25%,” he said in the interview. “That’s important, because now you have individuals that may not have any symptoms that can contribute to transmission, and we have learned that in fact they do contribute to transmission.”

This story was originally published May 28, 2020 at 10:29 AM with the headline "How many people have coronavirus but no symptoms? An alarming number, experts say."