"COVID-19 Symptoms vs. the Flu, a Cold or Allergies"
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 5 days,
so almost a week goes by when you’re infected,
and potentially infectious, before you even know it.
About 98% 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% and 70% of patients, respectively,
based on an analysis of more than 50,000 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 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% 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%), which involved difficulty getting enough oxygen,
or critical (5%), encompassing respiratory failure,
septic shock, and multi-system organ failure.
About half of those critical cases died.
So about 80% mild, 15% severe, and 5% critical,
though that doesn’t include all the asymptomatic cases that escaped
detection completely and never become confirmed cases at all.
Because as many as 4/5 of cases are asymptomatic,
the risk of dying after being infected may end up
ranging from 1 in a 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 that 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.