The symptoms of Covid-19 vary greatly. Typical symptoms of fever, shortness of breath, and chest pain are not seen in all cases. Atypical symptoms include intestinal complaints, loss of the senses of smell and/or taste, or mental confusion.
Covid-19, SARS-CoV-2, symptoms, fever, CDC, WHO, incubation period
First, let’s review the description of Covid-19 symptoms
U.S. Centers for Disease Control:
“People with COVID-19 have had a wide range of symptoms reported – ranging from mild symptoms to severe illness.” 
“Symptoms may appear 2-14 days after exposure to the virus. People with these symptoms may have COVID-19:
Shortness of breath or difficulty breathing
New loss of taste or smell
“This list is not all possible symptoms. Other less common symptoms have been reported, including gastrointestinal symptoms like nausea, vomiting, or diarrhea.” 
Another list of symptoms on the CDC website is here:
Shortness of breath
Myalgia (muscle aches, body aches)
Tiredness or fatigue”
Notice the wide range of symptoms. Covid-19 is able to infect a wide range of different organs: lungs, heart, kidney, intestines, cells lining blood vessels, and cells in the nervous system. This accounts for the wide range of symptoms. Not every patient has respiratory symptoms (shortness of breath, etc.) and not every patient has a fever.
The CDC also warns people of the following “emergency warning signs”:
“Look for emergency warning signs for COVID-19. If someone is showing any of these signs, seek emergency medical care immediately
• Trouble breathing
• Persistent pain or pressure in the chest
• New confusion
• Inability to wake or stay awake
• Bluish lips or face” 
These emergency symptoms are due to respiratory distress (bluish coloring, trouble breathing) and/or reduced oxygenation to the brain (new confusion, inability to wake). Pain or pressure in the chest could be due to respiratory or heart problems. Covid-19 can affect the heart (less common) or the lungs (most common). Symptoms vary greatly.
The incubation period of a disease is the time from when you are first infected to the time that you first begin to have symptoms. Lauer, et al. (Annals of Internal Medicine, 2020) found the following:
“The median incubation period was estimated to be 5.1 days (95% CI, 4.5 to 5.8 days), and 97.5% of those who develop symptoms will do so within 11.5 days (CI, 8.2 to 15.6 days) of infection. These estimates imply that, under conservative assumptions, 101 out of every 10 000 cases (99th percentile, 482) will develop symptoms after 14 days of active monitoring or quarantine.” 
The incubation period is almost certainly in the range of 4.5 to 5.8 days, and the vast majority of persons will begin to have symptoms within 11.5 days; 99% within 14 days. The median value is 5.1 days for the incubation period, meaning half of infected persons will show symptoms by 5.1 days.
Review the difference between mean or average and median here. Median is used in the above study because the numbers are right skewed: there will be a few persons who take much longer to show symptoms going forward, but the starting point can be no earlier than the day of infection, so the numbers stretch out to the right (forward in time). This gives the distribution of numbers a “right skew”, making median a better value to use than mean (average).
World Health Organization
Please review this “Advice for Public” from the WHO .
In summary, WHO recommends:
* Handwashing and alcohol-based hand sanitizers
* 1 meter (3 feet) distance between self and others
* Avoid crowded places
* Avoid touching face with hands
* Cover mouth when coughing
* Self-isolate even with minor symptoms
* Call your doctor or hospital FIRST, if you have symptoms
* Keep up to date on newest information
Health authorities in the U.S. recommend 2 meters (6 feet) distance between persons whenever possible. Hands can pick up the virus from objects, and then pass the virus into the body through mouth, nose, or eyes; therefore, people should avoid touching their face with their hands. Calling a doctor or hospital first avoids the problem of many persons sitting for a long time in a waiting area; this would spread the disease further. Sometimes, the advice by phone will be to self-isolate, and not to come to the doctor or hospital.
Chinese CDC Study
China has its own Centers for Disease Control. Their Novel Coronavirus Pneumonia Emergency Response Epidemiology Team did a study on the prevalence of the disease. They used three categories: mild, severe, critical, with mild comprising 80.9% of patients . This study is the reason for the press reports saying that 80 or 81% of cases are “mild”. However, in this categorization “mild” includes patients with “mild pneumonia” and “lung infiltrates” of less than 50%, as well as other symptoms which most patients would not consider to be mild. Later studies used a fourth category of “ordinary” or “moderate” instead of one overly-large category of mild.
Covid Mythbusting: That 80% of cases are mild. False. This claim is due to the above-discussed study which uses an unreasonably broad categorization for mild, with no category between mild and severe. Pneumonia with lung infiltrates of less than 50% should not be called “mild”. These types of cases can easily progress to death.
Other oft-cited claims also have their source in the above study. The study found “an overall case fatality rate of 2.3%” , which has not proven to be correct when larger data sets are examined. The current case fatality rate in the U.S. (total deaths/total cases) is 5.95%, and for the world data is 6.56% .
Symptoms of Covid-19 vary greatly. Mild symptoms can progress rapidly to a life-threatening condition. Follow guidelines from the CDC and WHO, and contact your health care provider at first sign of symptoms. Practice good hygiene and social distancing.
Ronald L Conte Jr
Note: the author of this article is not a doctor, nurse, or healthcare provider.
1. CDC.gov, Symptoms of Coronavirus.
2. Lauer, Stephen A., et al. “The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: estimation and application.” Annals of internal medicine (2020).
3. World Health Organization, WHO.int, Advice for the Public.
4. Surveillances, Vital. “The epidemiological characteristics of an outbreak of 2019 novel coronavirus diseases (COVID-19)—China, 2020.” China CDC Weekly 2.8 (2020): 113-122.
5. Worldometers, Coronavirus, retrieved 5/18/2020 10:00 a.m.