5. Diagnosis of COVID-19
The diagnosis was based on a set of clinical criteria recommended by the National Health Commission of the People’s Republic of China and the National Administration of Traditional Chinese Medicine [20].

5.1. Suspected Cases
The cases comply with any item of A and any two items of B, or with 3 items of B as follows. (A) Epidemiological history: within two weeks before disease onset, 1. have a history of travel or residence in the district with case report; 2. have contacted the patients positive with nucleic acid detection; 3. have contacted with the patients with fever and respiratory symptoms from the district with case report; 4. disease onset in clustering. (B) Clinical manifestations: 1. Have fever and/or respiratory tract symptoms; 2. Have pneumonia with image characteristics mentioned above; 3. In early stage of the disease, have normal or decreased total number of leukocytes, or decreased lymphocyte count.

5.2. Confirmed Cases
The unconfirmed cases met the criteria of the suspected cases and are identified positive with SARS-CoV-2 RNA, by real-time RT-PCR or gene sequencing, from the sputum, throat swab, lower respiratory tract secretion, or other samples collected from patients.

5.3. Clinical Typing of the Confirmed Cases
Mild cases: have mild symptoms, no pneumonia manifestation in chest image;
Common cases: have fever, respiratory symptoms, and pneumonia manifestation in chest image;
Severe cases: comply with any item of the follows. (A) dyspnea, respiratory rate ≥30 times/min; (B) at resting state, finger oxygen saturation ≤ 93%; (C) PaO2/FiO2 ≤ 300 mmHg (1mmHg = 0.133 kPa, PaO2: arterial partial pressure of oxygen, FiO2: fractional concentration of inspired oxygen);
Critical cases: comply with any item of the follows. (A) show respiratory failure and mechanical ventilation is required; (B) present with shock; (C) combine with other organ failure needing Intensive Care Unit (ICU) monitoring and treatment; (D) chest imaging shows multilobe lesions or progress of lesion focus within 48 h ≥ 50%; (E) combine with other clinical conditions requiring hospitalization.