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What Happens When a Coronavirus Infection Becomes Severe

Lung inflammation can make it difficult for some COVID-19 patients to breathe

spinner image A picture shows a monitor with a breathing machine on an intubated and sedated patient infected with COVID-19.
THOMAS COEX/AFP via Getty Images

The majority of people who get COVID-19, the illness caused by the new coronavirus, experience mild symptoms, if any at all, and are able to recover at home. But a fraction of the infected population faces a far worse reality — one that can involve severe sickness, even death.

"And right now, we have no good explanation for why,” says Robert Dickson, M.D., an assistant professor in the Division of Pulmonary and Critical Care Medicine in the Department of Medicine at the University of Michigan. “We can't predict which of these patients will basically get the sniffles, and which ones are going to need life support with a mechanical ventilator.”

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Older adults and people with underlying health conditions are at increased risk for more critical cases of coronavirus, health experts say. Even still, a report from the Centers for Disease Control and Prevention (CDC) shows plenty of young adults also are being hospitalized with difficulty breathing and other life-threatening symptoms.

Coronavirus symptoms

Mild COVID-19 cases:

  • Fever
  • Cough
  • Shortness of breath

People may also experience:

  • Chills
  • Repeated shaking with chills
  • Muscle pain 
  • Headache
  • Sore throat
  • New loss of taste or smell

COVID-19 emergency warning signs:

  • Trouble breathing
  • Persistent pain or pressure in the chest
  • New confusion or inability to arouse
  • Bluish lips or face

Source: Centers for Disease Control and Prevention

Here's what happens to the body when a mild case of COVID-19 turns serious:

Inflammation in the lungs makes it hard to breathe

Health experts suspect the coronavirus enters the body through the nose or mouth by way of small droplets that are passed when an infected person coughs or sneezes. Like most respiratory viruses, the infection “seems to start in the upper respiratory tract” — the back of the throat and the nose — and triggers symptoms that are typical of other upper respiratory infections, including fever and cough, Dickson says.

In some people, however, the disease moves down the respiratory tract and settles in the lungs, where it can cause “intense inflammation” (pneumonia) in the tiny air sacs. These sacs are where gas exchange takes place between the lungs and the bloodstream.

Most of the time, this gas exchange — oxygen into the body and carbon dioxide out — occurs easily, Dickson explains. However, “when you have an intense pneumonia, like COVID-19 is causing, those air spaces fill up with pus, they fill up with inflammation,” he says. And thicker pus-filled sacs make it more difficult for oxygen to pass from the lungs into the blood. Essentially: It becomes hard for a person to breathe.

Some patients need help breathing

When a patient starts to experience difficulty breathing, health care providers turn to “a ladder of interventions,” Dickson explains. Sometimes, a few liters of oxygen delivered through a tube that rests below the nose is all a patient needs to recover. If the damage to the lungs is more severe, a higher, faster flow of oxygen can help. In other instances, patients need breathing assistance from a mechanical ventilator.

The problem, Dickson notes, is that even though most people with COVID-19 are able to recover at home “or just with a little bit of extra oxygen,” many “end up needing more aggressive life support” while the body tries to heal itself. And they need this support for an extended period of time.

"We're finding that a lot of these patients need to be on the ventilator for two weeks or more, which is a very long time by ICU [intensive care unit] standards. And that is contributing to the crisis of ICU utilization,” Dickson says.

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A report released by the Office of Inspector General for the U.S. Department of Health and Human Services found that hospitals across the country are concerned about potential shortages of ICU beds and specialized staff to care for patients with life-threatening cases of COVID-19.

"It's not like someone's admitted to an ICU and we can turn around and get them out of there in a few days. Our ICUs are filling up because they need this life support for so long,” Dickson adds.

Recovery possible even with life-threatening illness

Medical experts are not aware of anything that can help prevent mild symptoms of COVID-19 from worsening, but it's “an active area of research,” Dickson says.

"Right now, the best advice we have is to avoid getting the infection in the first place. And this is all of the things we're hearing: social distancing; handwashing; don't touch your face, your mouth, your nose,” he adds.

It's also important to keep in mind that patients who get really sick from COVID-19 can recover.

"We absolutely have cases of people who get through it, who clear the viral infection, the inflammation subsides, the lung injury resolves,” Dickson says. “It's certainly scary and certainly life-threatening … but there is hope.”

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