COVID-19: An overview and a clinical update

Table 1 Classification of clinical types of coronavirus disease-2019 patients

Clinical types	Symptoms/clinical markers
Asymptomatic	Individuals who test positive for SARS-CoV-2 by COVID-19 nucleic acid test. Without any clinical symptoms and signs, and chest imaging is normal.
Mild	Presence of various signs and symptoms of COVID-19 (e.g., fever, fatigue, myalgia, cough, headache, sore throat, runny nose, sneezing), or digestive symptoms (nausea, vomiting, abdominal pain, diarrhea) without shortness of breath or abnormal chest imaging.
Moderate	Presence of pneumonia (frequent fever, cough) with no obvious hypoxemia (SpO2 ≥ 94% on room air at sea level); chest CT with lesions.
Severe	Patients with respiratory frequency > 30 breaths/minute; pneumonia with hypoxemia (SpO2 < 94%)on room air at sea level; a ratio of the arterial partial pressure of oxygen to fraction of inspired oxygen (PaO2/FiO2) < 300 mmHg or lung infiltrates > 50%.
Critical	Acute respiratory distress syndrome may have shock, encephalopathy, myocardial injury, heart failure, coagulation dysfunction, acute kidney injury, and/or multiple organ dysfunctions.

SARS-CoV-2: Severe acute respiratory syndrome -coronavirus -2; COVID-19: coronavirus disease-2019; CT: Computed tomography; SpO_2: Saturation of oxygen; FiO_2: Forced inspiratory oxygen.