From the WebMD Archives

Aug. 11, 2020 -- A big chunk of people who catch COVID-19 -- maybe as many as 40%, by some estimates -- never develop noticeable symptoms.

They don’t run a fever. They don’t cough or feel short of breath, and they don’t get the strange panoply of other symptoms that can herald a COVID-19 infection like frostbite-like bumps on the skin, diarrhea, or the loss of smell or taste.

“It's a very big portion of people, and although they are silent without symptoms, internally, they are taking hits in there inside their body so they don't even know it,” says Eric Topol, MD, the founder and director of the Scripps Translational Research Institute in La Jolla, CA. Topol and his co-author Daniel Oran, recently reviewed the medical evidence on asymptomatic infections.

Researchers who have scanned the hearts and lungs of people who tested positive for COVID-19, but never felt ill, have seen telltale signs of distress.

In the lungs, scientists have reported cloudy white areas called “ground glass opacities” in asymptomatic patients. Ground glass opacities are also seen patients with more severe COVID-19.

Across four different studies of people with asymptomatic infections, about half have had ground glass opacities on CT scans.

One of those was a study of passengers on the Diamond Princess cruise ship, which was quarantined for 2 weeks off the coast of Japan. Ultimately, 712 passengers -- out of 3,700 on board -- tested positive. Almost half of them, 331, had no symptoms. Of those, 76 had their lungs examined by CT scan for a study. More than half had ground glass opacities, though they didn’t show as much damage as people who had symptoms.

Aileen Marty, MD, professor of infectious diseases at Florida International University, says the hazy areas are areas of inflammation. It’s a sign that the lung is sick. She has seen it for herself. In her hospitals, 67% of people who don’t feel ill but test positive for COVID-19 have some changes in their lungs that can be seen on CT scans.

Nobody knows exactly what those changes mean yet or whether they will persist and form scar tissue or simply heal and go away after the infection is gone.

“I think that if you're young and you have enough lung reserve, you’ve not going to miss it because you're still able to function perfectly fine,” Marty says. “It's kind of like, you know, they say you have long hair and you cut off a 2 inches. Most people might not even notice you cut your hair because you have so much hair.”

It’s not just adults. Two studies have reported the same pattern in children with asymptomatic COVID-19 infections in Wuhan, China.

It’s one reason the director of the Palm Beach County Health Department, Alina Alonso, MD, has cautioned county officials to be careful when reopening schools.

“They are seeing there is damage to the lungs in these asymptomatic children. ... We don’t know how that is going to manifest a year from now or 2 years from now,” Alonso told Palm Beach County commissioners at a July meeting. “Is that child going to have chronic pulmonary problems or not?”

Valentina Puntmann, MD, has wondered about long-term consequences of COVID-19 on the heart. Puntmann is an expert in heart imaging at the University Hospital Frankfurt in Germany. She and a team of researchers recently scanned the hearts of 100 patients who had recently recovered from COVID-19, including 18 who were asymptomatic. They found that 78 had signs of heart damage, including elevated levels of troponin, proteins released by the heart muscle when it is damaged. Not all of the asymptomatic patients had markers for heart damage, but a few who did had some of the highest levels measured in the study.

“We have found a significant group of asymptomatic patients with inflammation,” Puntmann said in an email to WebMD.

Puntmann says many of her recovered COVID-19 patients get tired easily and can’t exercise as hard as they want to. “We see this a lot,” she says.

Topol cautions that the study was small and that the results for asymptomatic patients weren’t detailed separately. He says it’s hard to draw conclusions about elevated troponin levels since normal hearts can have elevated troponin levels, too.

Certainly, he says, asymptomatic infections are ripe for more research.

“Who knows what other organs are being affected? We don't know,” he says, “ No one's ever looked.”

Show Sources

Anthony Fauci, MD, director, National Institute of Allergy and Infectious Diseases, Bethesda, MD.

Donna Farber, PhD, professor of microbiology and immunology; principle investigator, the Columbia Center for Translational Immunology, Columbia University, New York.

Aileen Marty, MD, professor of infectious diseases and travel medicine, Herbert Wertheim College of Medicine, Florida International University, Miami.

Eric Topol, MD, founder and director, Scripps Translational Research Institute, La Jolla, CA; editor-in-chief, Medscape.

Valentina Puntmann, MD, PhD, deputy head, senior clinical research fellow, Institute for Experimental and Translational Cardiovascular Imaging, DZHK Centre for Cardiovascular Imaging, University of Frankfurt, Germany.

Annals of Internal Medicine, June 2020.

Nature, August 2020.

JAMA Cardiology, July 2020.

Journal of Clinical Virology, June 2020.

Korean Journal of Radiology, July 2020.

Radiology: Cardiothoracic Imaging, March 2020.

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