Infectious Diseases

Coronavirus Disease 2019 (COVID-19)

  • Clinicals
  • Infectious Diseases
  • 2021-05-01 11:58:04
  • 10 minutes, 52 seconds

Coronavirus Disease 2019 (COVID-19)

Coronavirus disease 2019 or COVID-19 is an illness that is caused by a novel coronavirus now called severe acute respiratory syndrome coronavirus. In this case, Novel stands for a new discovered virus. It was first identified amid an outbreak of respiratory illness cases in Wuhan City, Hubei Province, China and reported to the WHO on December 31, 2019.

COVID-19 is an acronym derived from "coronavirus disease 2019." This name was chosen to avoid stigmatizing the virus's origins. On early February, 2020, the virus was given an official designation for the novel virus: severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)

Coronavirus Disease 2019 is a new disease and it's spread, severity, causes and extent is being studied.

It belongs to a large family of viruses that cause illnesses ranging from the common cold to more severe infections such as pneumonia, Middle East Respiratory Syndrome and severe acute respiratory syndrome.

Characteristics of coronavirus.

Coronaviruses belong to a family of enveloped, positive-sense, single-stranded RNA (+ssRNA) viruses.

The SARS-CoV 2 (Covid-19) virion has a diameter of approximately 1,250 nm , and its genome ranges from 26 to 32 kilobases. Coronavirus is the largest for an RNA virus.

SARS-Coronavirus 2 has 5 structural proteins which are:

  1. spike (S),
  2. envelope (E),
  3. membrane (M),
  4. nucleocapsid (N), and
  5. hemagglutinin-esterase (HE).

The neucleocapsid(N) protein holds the ribonucleicacidgenome, and the spike (S), envelope (E,) and membrane (M) proteins create the viral envelope.

The S protein, together with hemagglutin-esterase (HE), is responsible for the entry of the virion into the cell. S protein is a club-shaped surface projection, giving the virus its characteristic crown-like appearance when seenuner an electron microscopy.

The S protein in this SARS-CoV 2 binds to the host cell through an enzyme known as angiotensin-converting enzyme 2 (ACE2)  and basigin (BSG). Angiotensin-converting enzyme 2 (ACE2) is expressed by epithelial cells of the intestine, kidney, blood vessels, and most abundantly in type II alveolar cells of the lungs.

This viral spike protein induces a drop in the levels of ACE2 in human cells, which might be the cause of  lung damage.

Learn more about these coronaviruses, their strains and structure in our article here.

It has been reported that COVID-19 has a fatality rate of about 2% making it clinically milder than MERS or SARS in severity and case fatality rate. 

COVID-19 has been confirmed in more than 137,000 individuals and has resulted in more than 5,000 deaths. More than 100 countries have reported laboratory-confirmed cases of COVID-19.

The Centers for Disease Control and Prevention (CDC) has stated that more cases of COVID-19 are likely to be confirmed in the United States in the near future. They also anticipate widespread SARS-CoV-2 community spread and that most of the US population will be exposed to the virus in coming months.

The CDC has postulated that this situation could result in large numbers of patients requiring medical care concurrently, resulting in overloaded public health and healthcare systems and, potentially, elevated rates of hospitalizations and deaths. The CDC advises that non-pharmaceutical interventions will serve as the most important response strategy in attempting to delay viral spread and to reduce disease impact.

Read more about the infection cycle of COVID-19 here.

Who is at risk of getting coronavirus Disease 2019?

Individuals who are at high risk of infection include;

  • Persons in areas with ongoing local transmission,
  • Healthcare workers caring for patients with COVID-19,
  • Close contacts of infected persons, and
  • Travelers returning from locations where local spread has been reported.

Severe cases had mostly been reported in adults older than 40 years old with significant comorbidities and skewed toward men,

What are the signs and symptoms of coronavirus disease 2019?

The clinical features of COVID-19 range from asymptomatic or mild symptoms to severe illness.

Symptoms may develop 2 days to 2 weeks following exposure to the virus

The most common signs and symptoms are;

  • Fever (98%),
  • Cough (76%) and
  • Myalgia,
  • Shortness of breath,
  • Fatigue/Malaise (44%).
  • Headache, sputum production, and diarrhea occur less common.

Individuals infected were characterized by the development of dyspnea in 55% of patients and lymphopenia in 66%. All those who had pneumonia had abnormal lung imaging findings.

When examining a patient with fever and acute respiratory illness one should obtain information on a history of travel or exposure to an person who recently returned from China.

  • 80% of infections are mild or asymptomatic
  • 15% are severe infections that require  oxygen therapy
  • 5% are critical infections that require ventilation.

Route of transmission

Coronaviruses are zoonotic viruses. This simply means that they are transmitted to humans through animals. The natural reservoir for SARS-CoV 2 is thought to be horseshoe bats or Malayan pangolins. This is because of the close genetic similarity to CoV strains that are found in these animals.

Once in humans, the virus is transmitted mainly via direct hand-to-face contact from infected surfaces or inhalation of aerosol droplets from the coughing or sneezing of symptomatic individuals.

Larger droplets spread about 1 meter (3 ft) and drop towards the ground, while smaller droplets can travel as an aerosol cloud more than 2 meters (6 ft) from the infected individual and remain viable in the air for up to 3 hours under the right conditions.

The virus that causes COVID-19 probably emerged from an animal source, but is now spreading from person to person. It also may be possible that a person can get COVID-19 by touching a surface or object that has the virus on it and then touching their own mouth, nose, or possibly their eyes.

Transmission is believed to occur via respiratory droplets from coughing and sneezing, as with other respiratory pathogens, including influenza and rhinovirus.

According to the WHO, the spread of SARS-CoV-2 in China seems to be largely limited to family members, healthcare providers, and other close contacts. Severe cases in China have mostly been reported in adults older than 40 years old with significant comorbidities and have skewed toward men. Few young children have been identified and those infected seem to have mild illness.

Asymptomatic patients or patients with no symptoms are still able to transmit infection.

Many of the initial cases were associated with direct exposure to live markets, while subsequent cases were not. This further gives a clue about the case for human-to-human transmission.

The incubation time for new infections is 5.2 days, with a range of 4.1-7 days. The longest time from infection to symptoms seemed to be 12.5 days. The epidemic had been doubling approximately every 7 days, and the base reproductive number was 2.2 meaning every patient infects an average of 2.2 others.

Currently, approximately 40% of the cases are “mild” with no pneumonia symptoms. Another 40% were “moderate” with symptoms of viral pneumonia, 15% were severe, and 5% critical. During the course of the illness, 10%-12% of cases that initially presented as mild or moderate illness progressed to severe, and 15%-20% of severe cases eventually became critical.

The mean time from exposure to symptoms was 5-6 days.

Patients with mild cases seem to recover within 2 weeks, while patients with severe infections may take 3-6 weeks to recover.

Deaths were observed from 2-8 weeks following symptom onset.

Note that, patients can shed virus 1-2 days before symptoms appear therefore the infectious period ranges from 2 days before the onset of symptoms up to 2–3 days after their resolution.

SARS-CoV 2 is highly contagious due to the production of high viral loads and efficient shedding of virions from the upper respiratory tract. However, asymptomatic individuals are also contagious, albeit to a slightly lesser degree.

The virus remains infectious on surfaces outside a host, especially on the ground, from a few hours up to a few days. Its life span will vary depending on the type of surface, humidity and temperature.

Diagnostic testing

Real-time reverse transcription–polymerase chain reaction (rRT-PCR) assay can be used to diagnose the virus in respiratory and serum samples from clinical specimens.

Signs and symptoms of coronavirus disease 2019 (COVID-19) may overlap with those of other respiratory infections; therefore, it is important to perform laboratory testing to specifically identify symptomatic individuals infected with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). 

There are 3 types of tests that may be utilized to determine if an individual has been infected with SARS-CoV-2: 

  • Viral nucleic acid (RNA) detection 
  • Viral antigen detection 
  • Detection of antibodies to the virus  

Viral tests (nucleic acid or antigen detection tests) are used to assess acute infection, whereas antibody tests provide evidence of prior infection with SARS-CoV-2. Home sample collection kits for COVID-19 testing have been available by prescription, in December 2020, the LabCorp Pixel COVID-19 Test Home Collection Kit became the first to receive an FDA EUA for nonprescription use. 

Laboratory findings in patients with COVID-19

Lactate dehydrogenase and ferritin levels are commonly elevated.

29% developed an acute respiratory distress syndrome (ARDS), and ground-glass opacities are common on CT scans.

Leukopenia, leukocytosis and lymphopenic pictures are seen in early cases.

In patients who develop pneumonia, a chest CT will show bilateral involvement, multiple areas of consolidation, and ground-glass opacities.

In the case of ARDS, arterial blood gas analysis shows hypoxemic respiratory failure with respiratory alkalosis, and a chest CT can show diffuse bilateral infiltrates, air bronchograms, atelectasis, and even pleural effusion.

Chest x-ray may reveal pulmonary infiltrates.

  • Upper respiratory tract
    • Nasopharyngeal swab (easiest method, recommended for mild or asymptomatic suspected cases)
    • Throat swab
  • Lower respiratory tract
    • Bronchial and tracheal secretions
    • Bronchoalveolar lavage for patients receiving invasive mechanical ventilation.
    • Sputum (for patients with productive cough)


About 1 in 6 people with COVID-19 clinically deteroriate and develop a complication in the 2nd week of illness. These patients may develop dyspnea, high fever, chest pain, hemoptysis, respiratory crackles, and progressive respiratory insufficiency that could potentially lead to death.

The most common complications of COVID-19 reported are interstitial pneumonia and acute respiratory distress syndrome (ARDS). Others include cardiac injury, arrhythmia, septic shock, liver dysfunction, acute kidney injury, and multi-organ failure.

Risk factors for the severe form of the illness is:

  • Immunosuppression (ie, cancer, AIDS/HIV infection,  use of immunosuppressant, etc.)
  • Age (over 65 years old)
  • Chronic diseases and
  • Pregnanct women

The expression of ACE2 is highly increased in patients with diabetes mellitus or hypertension being treated with ACE inhibitors, which produces an upregulation of ACE2.

Treatment of COVID-19

No specific antiviral treatment is recommended for COVID-19. Infected patients should receive supportive care to help alleviate symptoms.

Vital organ function should be supported in severe cases.

No drugs or biologics have been proven to be effective for the prevention or treatment of COVID-19 but a number of antiviral agents, immunotherapies, and vaccines are being investigated and developed as potential therapies.

Hydroxychloroquine drug has also been subjected to clinical trials over its effectiveness..

Vaccines for SARS-CoV-2 have been developed and used worldwide in the quest to curb the spread.

The most commonly administerd vaccine is Astrazeneca. Learn more about this vaccine in our recent article here

Once hospitalized, supportive care and acute measures should be applied as necessary for complications, such as:

  • Oxygen therapy for patients who develop respiratory distress, hypoxemia, or shock
  • Empiric antimicrobials in the case of sepsis or secondary pneumonia
  • Advanced oxygen therapy, ventilatory support, and conservative fluid management in the case of acute respiratory distress syndrome
  • Fluid bolus and vasopressors in the case of septic shock

For the latest management guidelines, see the “WHO interim guidance on clinical management of severe acute respiratory infection when novel coronavirus (nCoV) infection is suspected.

General measures for prevention of viral respiratory infections include:

Wash hands with soap and water for at least 20 seconds. An alcohol-based hand sanitizer may be used if soap and water are unavailable.

Avoid touching their eyes, nose, and mouth with unwashed hands.

Avoid close contact with sick people.

Sick people should stay at home to prevent spread.

Cover yourself when coughing or sneezing with a tissue, followed by disposal of the tissue in the trash.

Clean and disinfect frequently touched objects and surfaces regularly.

Infection control

Quarantine and isolation: Depending on official risk assessment, measures may range from home isolation to quarantine of entire communities.

Patients who are under investigation for COVID-19 should be evaluated in a private room with the door closed and should wear a surgical mask.

Observe all other standard contact and airborne precautions.

All the treating healthcare personnel should wear eye protection.

What should I do if I recently traveled from an area with ongoing spread of COVID-19?

If you have traveled from an affected area, there may be restrictions on your movements for up to 2 weeks. If you develop symptoms during that period (fever, cough, trouble breathing), seek medical advice.

Call the office of your health care provider before you go, and tell them about your travel and your symptoms. They will give you instructions on how to get care without exposing other people to your illness.

While sick, avoid contact with people, don’t go out and delay any travel to reduce the possibility of spreading illness to others.

Should I wear a mask to protect myself?

Only wear a mask if you are ill with COVID-19 symptoms (especially coughing) or looking after someone who may have COVID-19. Disposable face mask can only be used once. If you are not ill or looking after someone who is ill then you are wasting a mask. There is a world-wide shortage of masks, so WHO urges people to use masks wisely.

References: CDC. 2019 Novel Coronavirus, Wuhan, China. CDC. Available at , CDC. Symptoms of Coronavirus. CDC. Available at May 13, 2020;

Daniel Ogera

Medical educator, passionate about simplifying difficult medical concepts for easier understanding and mastery by nursing and medical students.

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About this article:
  • Topic:Clinicals
  • Duration:10 minutes, 52 seconds
  • Subtopic:Infectious Diseases

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