Overview

This prospective cohort study aims to characterize the natural progression and outcomes of acute respiratory infections among patients presenting to fever clinics. At enrollment, patients' clinical symptoms, laboratory findings, and chest imaging data will be collected. Longitudinal follow-up will be conducted to evaluate disease progression, complications, and long-term outcomes.

As an observational study, no interventions are involved; all patients receive routine clinical management as directed by their attending physicians. This real-world study design enables the assessment of the natural course of acute respiratory infections and the identification of factors associated with clinical outcomes.

Eligibility

Inclusion Criteria:

• Age ≥ 18 years (based on official identification document).
• Presence of fever at the time of visit or within 24 hours prior to the visit, defined as a documented temperature of ≥37.3°C axillary/tympanic, ≥37.8°C orally, or ≥38.0°C rectally.
• The primary cause of fever, as determined by the attending physician, is a respiratory tract infection.
• Blood draw is required as part of standard clinical care.
• Ability to comprehend the study's purpose, procedures, and potential risks, and willingness to provide written informed consent.

Exclusion Criteria:

• Inability to provide independent informed consent due to impaired consciousness or other reasons.
• Inability to comply with the study procedures.
• Medical contraindications to blood sampling, such as severe coagulopathy (e.g., INR \> 3.0, platelet count \< 50 × 10⁹/L).
• Diagnosed with a terminal illness (e.g., advanced malignancy, severe multiple organ failure) and a life expectancy of less than 3 months.