The earliest cases of SARS-CoV-2 were identified as “pneumonia of unknown etiology”, which was defined as an illness of unknown etiology with 1. Fever with or without a recorded temperature 2. Radiographic evidence of pneumonia 3. Low or normal leukocyte count or low lymphocyte count during the early stage of disease and 4. No improvement or worsening symptoms after 3–5 days of antimicrobial treatment per standard clinical guidelines [61]. With increasing research and knowledge of the disease, diagnosis and treatment guidelines have been continuously updated. At present, the NHC has issued the fifth edition of the guidelines. However, because of a shortage of diagnostic reagents for SARS-CoV-2 detection, different guidelines or programs emphasized comprehensive analysis based on epidemiological history, clinical manifestations and imaging examinations in diagnosis.