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Overview and Spectrum of COVID-19

Last Updated: April 21, 2020

Overview and Spectrum of COVID-19
Summary Recommendations
  • The COVID-19 Treatment Guidelines Panel (the Panel) does not recommend the use of any agents for pre-exposure prophylaxis (PrEP) against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outside of the setting of a clinical trial (AIII).
  • The Panel does not recommend the use of any agents for post-exposure prophylaxis (PEP) against SARS-CoV-2 infection outside of the setting of a clinical trial (AIII).
  • The Panel recommends no additional laboratory testing and no specific treatment for persons with suspected or confirmed asymptomatic or presymptomatic SARS-CoV-2 infection (AIII).
  • At present, no drug has been proven to be safe and effective for treating COVID-19. There are insufficient data to recommend either for or against the use of any antiviral or immunomodulatory therapy in patients with COVID-19 who have mild, moderate, severe, or critical illness (AIII).
Rating of Recommendations: A = Strong; B = Moderate; C = Optional
Rating of Evidence: I = One or more randomized trials with clinical outcomes and/or validated laboratory endpoints; II = One or more well-designed, nonrandomized trials or observational cohort studies; III = Expert opinion


The COVID-19 pandemic has exploded since cases were first reported in China in January 2020. As of April 19, 2020, more than 2.4 million cases of COVID-19—caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection—have been reported globally, including >165,000 deaths. Cases have been reported in more than 180 countries, including all 50 states of the United States.1, 2

Individuals of all ages are at risk for infection and severe disease. However, the probability of fatal disease is highest in people aged ≥65 years and those living in a nursing home or long-term care facility.

Others at highest risk for COVID-19 are people of any age with certain underlying conditions, especially when not well-controlled, including:3-7

  • Hypertension
  • Cardiovascular disease
  • Diabetes
  • Chronic respiratory disease
  • Cancer
  • Renal disease, and
  • Obesity.

Clinical Presentation

The estimated incubation period for COVID-19 is up to 14 days from the time of exposure, with a median incubation period of 4 to 5 days.4,8,9 The spectrum of illness can range from asymptomatic infection to severe pneumonia with acute respiratory distress syndrome (ARDS) and death. In a summary of 72,314 persons with COVID-19 in China, 81% of cases were reported to be mild, 14% were severe, and 5% were critical.10 In a report of 1,482 hospitalized patients with confirmed COVID-19 in the United States, the most common presenting symptoms were cough (86%), fever or chills (85%), and shortness of breath (80%), diarrhea (27%), and nausea (24%).7 Other reported symptoms have included, but are not limited to, sputum production, headache, dizziness, rhinorrhea, anosmia, dysgeusia, sore throat, abdominal pain, anorexia and vomiting.

Common laboratory findings of COVID-19 include leukopenia and lymphopenia. Other laboratory abnormalities have included elevations in aminotransferase levels, C-reactive protein, D-dimer, ferritin, and lactate dehydrogenase.

Abnormalities in chest X-ray vary, but typically reveal bilateral multi-focal opacities. Abnormalities seen in computed tomography (CT) of the chest also vary, but typically reveal bilateral peripheral ground-glass opacities with the development of areas of consolidation later in the clinical course.11 Imaging may be normal early in infection and can be abnormal in the absence of symptoms.11

Diagnosis of SARS-CoV-2 Infection

Ideally, diagnostic testing would be conducted for all patients with a syndrome consistent with COVID-19, people with known high-risk exposures, and people likely to be at repeated risk of exposure, such as health care workers and first responders. For more information, see the Centers for Disease Control and Prevention (CDC) COVID-19 website.

CDC recommends that nasopharynx samples be used to detect SARS-CoV-2. Nasal swabs or oropharyngeal swabs may be acceptable alternatives.12 Lower respiratory tract samples have a higher yield than upper tract samples, but often they are not obtained because of concerns about aerosolization of virus during sample collection procedures.

While initial diagnostic tests for SARS-CoV-2 infection have relied on reverse transcriptase polymerase chain reaction platforms, more recent tests have included a variety of additional platforms. More than 20 diagnostic tests for SARS-CoV-2 infection have received Emergency Use Authorization by the Food and Drug Administration.13 Formal comparisons of these tests are in progress.

CDC has established a priority system for diagnostic testing for SARS-CoV-2 infection based on the availability of tests;14 the CDC testing guidance is updated periodically.

  • Priority 1: Hospitalized patients and symptomatic health care workers (to reduce the risk of nosocomial infections and maintain the health care system).
  • Priority 2: Individuals with symptoms who live in long-term care facilities, who are aged ≥65 years, or who have underlying conditions, and symptomatic first responders (to ensure those at highest risk of complications of infection are rapidly identified and triaged).
  • Priority 3: In communities experiencing high COVID-19 hospitalizations, critical infrastructure workers and other individuals with symptoms, health care workers and first responders, and individuals with mild symptoms (to decrease community spread and ensure the health of essential workers).

Of note, false-negative test results can occur. In people with a high likelihood of infection based on exposure history and/or clinical presentation, a single negative test does not completely exclude SARS-CoV-2 infection, and testing should be repeated.

Routes of SARS-CoV-2 Transmission and Standard Means of Prevention

The onset and duration of viral shedding and period of infectiousness are not completely defined. Asymptomatic or pre-symptomatic individuals infected with SARS-CoV-2 may have viral RNA detected in upper respiratory specimens before the onset of symptoms.15 Transmission of SARS-CoV-2 from asymptomatic individuals has been described.16-18 The extent to which this occurs remains unknown.


  1. World Health Organization. Coronavirus disease (COVID-2019) situation reports. 2020. Available at: Accessed April 9, 2020.
  2. Centers for Disease Control and Prevention. Coronavirus disease 2019 (COVID-19): cases in U.S. 2020. Available at: Accessed April 9, 2020.
  3. Wu C, Chen X, Cai Y, et al. Risk factors associated with acute respiratory distress syndrome and death in patients with coronavirus disease 2019 pneumonia in Wuhan, China. JAMA Intern Med. 2020. Available at:
  4. Guan WJ, Ni ZY, Hu Y, et al. Characteristics of coronavirus disease 2019 in China. N Engl J Med. 2020. Available at:
  5. Cai Q, Chen F, Luo F, et al. Obesity and COVID-19 severity in a designated hospital in Shenzhen, China. Preprints with the Lancet. 2020;[Preprint]. Available at:
  6. Centers for Disease Control and Prevention. Coronavirus disease 2019 (COVID-19): People who are at higher risk for severe illness. 2020. Available at: Accessed April 8, 2020.
  7. Garg S, Kim L, Whitaker M, et al. Hospitalization rates and characteristics of patients hospitalized with laboratory-confirmed coronavirus disease 2019 - COVID-NET, 14 states, March 1-30, 2020. MMWR Morb Mortal Wkly Rep. 2020;69(15):458-464. Available at:
  8. Li Q, Guan X, Wu P, et al. Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia. N Engl J Med. 2020;382(13):1199-1207. Available at:
  9. Lauer SA, Grantz KH, Bi Q, et al. The incubation period of coronavirus disease 2019 (COVID-19) from publicly reported confirmed cases: Estimation and application. Ann Intern Med. 2020. Available at:
  10. Wu Z, McGoogan JM. 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. Available at:
  11. Shi H, Han X, Jiang N, et al. Radiological findings from 81 patients with COVID-19 pneumonia in Wuhan, China: a descriptive study. Lancet Infect Dis. 2020;20(4):425-434. Available at:
  12. Centers for Disease Control and Prevention. Interim guidelines for collecting, handling, and testing clinical specimens from persons for coronavirus disease 2019 (COVID-19). 2020. Available at: Accessed April 8, 2020.
  13. Food and Drug Administration. Coronavirus disease 2019 (COVID-19) emergency use authorizations for medical devices. 2020. Available at: Accessed April 8, 2020.
  14. Centers for Disease Control and Prevention. Evaluating and testing persons for coronavirus disease 2019 (COVID-19). 2020. Available at: Accessed April 8, 2020.
  15. Pan Y, Zhang D, Yang P, Poon LLM, Wang Q. Viral load of SARS-CoV-2 in clinical samples. Lancet Infect Dis. 2020;20(4):411-412. Available at:
  16. Rothe C, Schunk M, Sothmann P, et al. Transmission of 2019-nCoV infection from an asymptomatic contact in Germany. N Engl J Med. 2020;382(10):970-971. Available at:
  17. Yu P, Zhu J, Zhang Z, Han Y, Huang L. A familial cluster of infection associated with the 2019 novel coronavirus indicating potential person-to-person transmission during the incubation period. J Infect Dis. 2020. Available at:
  18. Bai Y, Yao L, Wei T, et al. Presumed asymptomatic carrier transmission of COVID-19. JAMA. 2020. Available at: