COVID-19: The Basics

The Novel Coronavirus 2019, was first reported on in Wuhan, China in late December 2019.  The outbreak was declared a public health emergency of international concern in January 2020 and on March 11th, 2020, the outbreak was declared a global pandemic.  The spread of this virus is now global with lots of media attention.  The virus has been named SARS-CoV-2 and the disease it causes has become known as coronavirus disease 2019 (COVID-19).  This new outbreak has been producing lots of hysteria and false truths being spread, however the data surrounding the biology, epidemiology, and clinical characteristics are growing daily, making this a moving target.  This post will serve as a summary of what is currently known about the basics of COVID-19. 

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COVID-19 Compared to SARS, MERS, and Influenza [1][3][4]

  • Severe Acute Respiratory Syndrome – SARS-CoV (2002 – 2004)
    • 8,096 cases and 744 deaths (Case fatality rate 9.2%)
  • Middle Eastern Respiratory Syndrome – MERS-CoV (2012 to 2016)
    • 2,494 cases and 858 deaths (Case fatality rate 34.4%)
  • COVID-19 (Dec 2019 to Present)
    • As of May 4th, 2020, 3,571,615 cases and 250,134 deaths (Case fatality rate 7.0%) –> Updated Daily Stats from Johns Hopkins CSSE
      • The case fatality rate of COVID-19 is likely overinflated (As testing becomes more available and includes asymptomatic and mild cases, more realistic numbers will be available – i.e. as the exact denominator is unknown, it is unclear what the true rates of death are)
    • In one study [2], of 138 hospitalized patients with confirmed novel coronavirus-infected pneumonia (NCIP), the rate of hospital-associated transmission was:
      • Active Health Care Professionals: 40 (29%)
      • Hospitalized Patients: 17 (12.0%)
      • This suggests a 41% nosocomial spread
    • Influenza (Sept 2019 Up to Week Ending Feb 15th, 2020)
        • 29,000,000 cases 280,000 hospitalizations, with 16,000 flu related deaths (Case fatality rate 0.06%)

How Contagious is the Disease? = R0 (R nought)

  • R0 = One case of the disease will potentially spread to how many others
  • Below is a list of approximate R0 for various infections (These numbers can vary depending on which study you read, but give an idea of how transmissible different illnesses can be):
    • Measles = 12 – 18
    • Smallpox = 5 – 7
    • SARS = 2 – 5
    • Pandemic Flu = 2 – 4
    • COVID-19 = 2.2 – 3.9
    • Seasonal Flu = 0.9 – 2.1
    • MERS = 0.3 – 0.8

The Diamond Princess Cruise Ship [7]

  • Although, unfortunate, the Diamond Princess cruise ship gave us great insight into what the spread of COVID-19 looks like in an isolated environment
  • 3711 people on board with 355 cases confirmed (As of Feb 16th, 2020).  This gives an R0 of 2.28 for COVID-19
  • Deaths from COVID-19 was 7 out of 355 cases (Case Fatality Rate of 1.9%)

Signs and Symptoms of COVID-19

  • Incubation period is 2 – 14 days (Median 5 to 6 days)
  • Most common symptoms [5][6]:
  • Fever (83 – 98%)
    • Of 1099 pts with confirmed COVID-19, 43.8% of patients had fever at admission, but 88.7% developed fever during hospitalization
  • Dry cough (67.8% – 82%)
  • Dyspnea (≈33%)
  • May also have myalgias (11%), fatigue (38.1%) (i.e. similar to influenza), and sore throat (13.9%) [5][6]
  • A study out of China [Link is HERE], evaluated 204 patients with COVID-19 confirmed infection:
    • 99 patients (48.5%) presented with GI symptoms as their chief complaint
    • There was a variety of GI symptoms:
      • Anorexia: 83.8%
      • Diarrhea: 29.3%
      • Vomiting: 0.8%
      • Abdominal Pain: 0.4%
      • Since anorexia is so non-specific, if we remove this complaint 41/204 total cases (20%) were patients with GI specific complaints (i.e. diarrhea, vomiting, abdominal pain)
      • 7/204 (3.4%) had only digestive symptoms but no respiratory symptoms
    • Patients without digestive symptoms were more likely to be discharged than patients with digestive symptoms (60% vs 34.3%)
    • Patients with digestive symptoms also had a longer time from onset to hospital admission vs patients without digestive symptoms (9.0d vs 7.3d)
    • Theory proposed by authors: There is an up-regulation of ACE-2 expression in liver tissue
    • Digestive symptoms are also common in patients with COVID-19 and if we solely monitor for respiratory symptoms to establish case definitions for COVID-19, we may miss cases initially


Coronavirus in New York – From the Front Lines March 23rd, 2020 (Video Time: 35:59)


  1. Giwa A t al. Novel Coronavirus COVID-19: An Overview for Emergency Clinicians. Emerg Med Pract 2020. PMID 32105049
  2. Wang D et al. Clinical Characteristics of 138 Hospitalized Patients with 2019 Novel Coronavirus-Infected Pneumonia in Wuhan, China. JAMA 2020. PMID: 32031570
  3. American College of Emergency Physicians (ACEP). COVID-19 (Coronavirus) Clinical Alert. Feb 2020. [Link is HERE]
  4. Wu Z et al. Characteristics of and Important Lessons From the Coronavirus Disease 2019 (COVID-19) Outbreak in China: Summary of a Report of 72,314 Cases From the Chinese Center for Disease Control and Prevention. JAMA 2020. PMID: 32091533
  5. Yee J et al. Novel coronavirus 2019 (COVID-19): Emergence and Implications for Emergency Care. Infectious Disease 2020. [Link is HERE]
  6. Guan WJ et al. Clinical Characteristics of Coronavirus Disease 2019 in China NEJM 2020. [Epub Ahead of Print]
  7. Zhang Sheng et al. Estimation of the Reproductive Number of Nobel Coronavirus (COVID-19) and the Probable Outbreak Size on the Diamond Princess

For More Thoughts on This Topic Checkout:

Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami) and Mizuho Morrison, DO (Twitter: mizuhomorrison)

Cite this article as: Salim Rezaie, "COVID-19: The Basics", REBEL EM blog, March 1, 2020. Available at:

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