Early identification and Severity prediction of Acute Respiratory infectious disease has become a top priority for clinicians at department of infectious and respiratory diseases after COVID-19 broke out. This is a multicenter, prospective, and randomized study, which aims to figure out the best way of early identification and severity prediction of acute respiratory infectious diseases. Patients with suspected acute respiratory infectious diseases will be enrolled into this study and received two different diagnostic pathways.

Inclusion Criteria:

1. Patients aged between 18 and 80 years old

2. No limits in gender

3. Patients who are newly present with cough, sputum, or exacerbated with pyogenic sputum, with or without chest pain within 2 weeks;

4. Patients who meet at least one of the following 4 requirements:

   1. fever;
   2. Sign of pulmonary consolidation or wet wales
   3. WBC>10×10^9/L or <4×10^9/L;
   4. patchy, infiltrating shadows or interstitial changes, with or without pleural effusion on chest radiological examination.

Exclusion Criteria:

1. Highly suspected or diagnosed pulmonary non-infectious disease (Tumor, Immune disease, etc.) without evidence for infection;
2. Pathogen has been identified without evidence for co-infection;
3. Insufficiency of respiratory and blood samples;
4. Patients who are unable to collaborate due to physical or mental disorders;
5. Patients who have been engaged to other clinical trials;
6. Any conditions make it unsafe for the subject to participate;