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What does the clinical course of COVID-19 look like? It tends to start with fever and cough, but before then, the average incubation period—the time between the moment you get sufficiently exposed to the virus and the moment you start showing symptoms—seems to be about five days. So, almost a week goes by when you’re infected—and potentially infectious—before you even know it. About 98 percent of those who are going to start showing symptoms do so by day 12, which explains why people are typically asked to self-quarantine for two weeks after a potential exposure. After infection, apparent viral shedding may continue for more than a month (with an average of 20 days), though it’s not clear how contagious survivors are—if at all—during that extended time period.
The most common symptoms are fever and cough, experienced by about 90 percent and 70 percent of patients, respectively, based on an analysis of more than fifty thousand COVID-19 patients. In terms of less common symptoms, only about four in ten experience fatigue; three in ten cough up phlegm; and two in ten experience muscle aches. Only about one in ten suffer from gastrointestinal symptoms, such as nausea, vomiting, or diarrhea, or common cold-type symptoms, like a runny or stuffy nose, headache, or a sore throat. This is consistent with the regional concentration of ACE2—the receptors the virus latches onto—in the lungs, rather than the nose or throat (though in pangolins, ACE2 is found on their flicking anteater tongues).
Here’s a chart that can help you differentiate between COVID-19, the common cold, the flu, or seasonal allergies. The only COVID-19 symptom found predictive of a more severe course was difficulty breathing, which resulted in more than six times the odds of eventually having to be admitted into the ICU. That’s why that’s such an important symptom to catch early, and a red flag to immediately seek medical attention. If it’s going to strike, shortness of breath usually hits a week after symptoms begin.
The notion that the course of about 80 percent of cases are “mild” was derived from an analysis by the Chinese CDC that was based on nearly 45,000 confirmed cases. While there are certainly mild and even asymptomatic cases, it’s important to understand what “mild” means to the Chinese CDC. Its definition of mild included those with so-called “walking pneumonia,” meaning pneumonia not dire enough to require supplemental oxygen or hospitalization, but pneumonia nonetheless—certainly not the “common cold”-type courses people might think of when they hear the word mild—though the cases were at least mild enough that people should be able to treat themselves at home.
The remaining 20 or so percent of confirmed cases were classified as severe (about 15 percent), which involved difficulty getting enough oxygen, or critical (5 percent), encompassing respiratory failure, septic shock, and multisystem organ failure. About half of those critical cases died. So, about 80 percent mild, 15 percent severe, and 5 percent critical––though that doesn’t include all the asymptomatic cases that escaped detection completely, and never became confirmed cases at all.
Because as many as four-fifths of cases are asymptomatic, the risk of dying after being infected may end up ranging from 1 in 1,000 to about 1 in 300, though if you do show symptoms, the risk of death may be more like 1 in 150.
On autopsy, the respiratory surface of the lung under a microscope appears obliterated by scar tissue. Pulmonary fibrosis (lung scarring) is expected to become one of the long-term complications among survivors of serious COVID-19 infection. A six-month follow-up of SARS survivors found about one in three showed evidence of scarring on chest x-ray, and up to one in six suffered a significant impairment in lung function.
Death from COVID-19 comes from progressive “consolidation” of the lung, meaning your lungs start filling up with something other than air. In the case of regular pneumonia, that’s largely pus. In COVID-19 pneumonia, postmortems show you drown in lungs that are “filled with clear liquid jelly.”
But the good news is that there are modifiable risk factors for death and disability from COVID-19, meaning things you have control over that can reduce your risk, which we’ll explore next.
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