This nationwide, multicenter observational study will establish and improve a hospital-based clinical surveillance and early warning system for respiratory syndrome pathogens. Clinical data and biospecimens generated during routine care will be collected from participating medical institutions every two weeks to monitor pathogen trends, support risk assessment, and provide evidence for prevention and control measures.

This study will enroll eligible patients with respiratory syndrome from fever clinics, emergency departments, outpatient clinics, and inpatient wards in participating hospitals across seven administrative regions in China. Standardized clinical data, including demographic information, symptoms, diagnoses, laboratory tests, medication orders, oxygen therapy, hospitalization, ICU admission, and outcomes, will be reported through encrypted data channels every two weeks. For eligible participants meeting the tiered diagnostic criteria, respiratory samples and clinically remaining biospecimens will be tested using routine pathogen testing, multiplex PCR or targeted sequencing, metagenomic next-generation sequencing, antibody testing, cytokine testing, and exploratory multi-omics assays as clinically appropriate. The study aims to generate national and regional surveillance reports and support early warning, pathogen identification, and prevention and control strategies.

Inclusion Criteria:

• Patients with respiratory syndrome: Eligible patients are those diagnosed with respiratory syndrome based on the predefined data dictionary and the following ICD-10 (International Statistical Classification of Diseases, 10th Revision) diagnosis codes: R05, R50, J00, J01, J02, J03, J04, J06, J07, J08, J09, J10, J11, J12, J13, J14, J15, J16, J17, J18, J20, J21, J98.414, and J98.802.

• Patients with respiratory syndrome: Eligible patients are identified using the following search criteria. Patients meeting any one of the following criteria should be included:

  1. Medical history (History of Present Illness): Positive test result for a respiratory syndrome-related pathogen.

  2. Laboratory testing: Positive test result for a respiratory syndrome-related pathogen.

  3. Medication: Receipt of any of the following antiviral agents:

     Nirmatrelvir/Ritonavir Leritrelvir Xiannuotewei/Ritonavir Molnupiravir Azvudine Deuremidevir

  4. Diagnosis: Diagnosis containing the term "respiratory tract infection."

Exclusion Criteria:

• Participants who may compromise the study results: Patients who are unable to provide a specimen or whose specimen volume is insufficient for laboratory testing.
• Participants who are unable to comply with study procedures.

Patients with respiratory syndrome treated in fever clinics, emergency departments, outpatient clinics, or inpatient wards of participating medical institutions across China.