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For further information, see CMDT Part 32-06: Common Viral Respiratory Infections

Key Features

Essentials of Diagnosis

  • Asymptomatic in approximately 20–35% of adults and most children

  • When symptomatic, adults often have upper respiratory tract illness with fever and cough

  • Advanced pulmonary complications (pneumonia, acute respiratory distress syndrome [ARDS]) occur with fulminant disease

  • Mortality of 1–21% (varied by geographic area and strain)

  • High predilection for the elderly, the immunocompromised, those with chronic diseases, those living in crowded conditions

General Considerations

  • A case tally and other current information are available through

  • Incubation period: ranges from 2 to 24 days with an average of about 5 days

  • Transmission

    • Principal mode: respiratory droplets

    • R0 is the basic reproductive number signifying the number of contacts infected by one infectious individual

      • Calculations of R0 for SARS-CoV-2 have varied

      • However, the true R0 likely lies somewhere between 2 and 3

    • Reported rates of transmission are 5% for close contacts and 10–40% for household contacts

    • Presymptomatic spread accounts for many cases, and the viral load for SARS-CoV-2 is highest the day before symptoms develop

    • In utero transmission is reported but appears to be rare

    • In general, the virus does not appear to be transmitted in breastmilk

  • Risk factors

    • Age

    • Chronic conditions (diabetes; obesity; hypertension; chronic heart, lung, or kidney disease; and prior stroke)

    • Cigarette smoking

    • Symptomatic disease appears to develop in men more often than in women

Clinical Findings

Symptoms and Signs

  • Most infected individuals are asymptomatic

  • Adults can manifest a wide range of symptoms from mild to severe illness that typically begin 2–14 days after exposure

  • Symptomatic patients may have cough, fever, chills/rigors, or myalgias

  • The presence of dyspnea is variable, but it is common in severe infection

  • No one symptom should be used as a discriminant for disease

  • Less frequent symptoms include rhinitis, pharyngitis, abdominal symptoms such as nausea and diarrhea, headaches, anosmia and cacosmia, and ageusia and cacogeusia

  • It appears that 15–20% of adults require hospitalization and 3–5% require critical care

Differential Diagnosis

  • Upper respiratory infection

  • Seasonal influenza infection

  • Secondary hemophagocytic lymphohistiocytosis


Laboratory Findings

  • Neutrophilia, absolute lymphopenia, and an increased neutrophil to lymphocyte ratio

  • Elevated liver biochemical tests and total bilirubin

  • Serum markers of systemic inflammation are increased

    • Lactate dehydrogenase

    • Ferritin

    • C-reactive protein

    • Procalcitonin

    • Interleukin 6 (IL-6)

  • A coagulopathy often is seen

  • Elevated von Willebrand factor (VWF) antigen

  • Elevated D-dimer

  • Fibrinogen levels are higher than in disseminated intravascular coagulation


  • Early in the disease course,

    • Neither chest radiographs nor chest CT scans provide diagnostic utility

    • Both may be normal


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