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.

This prospective cohort study aims to characterize the natural history and outcomes of acute respiratory infection in patients presenting to fever clinics. Upon enrollment, patients' clinical symptoms, laboratory parameters, and chest imaging data will be collected. Subsequent longitudinal follow-up will be performed to assess disease progression, complications, and long-term outcomes.

As an observational study, no interventions are implemented; all patients receive standard-of-care management as determined by their attending physicians. This real-world study design allows for the evaluation of the natural progression of acute respiratory infections and the identification of factors associated with clinical outcomes.

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.

Patients presenting to fever clinics with acute respiratory infections, aged 18 years or older, who provide informed consent. Both sexes are eligible. Participants are observed under standard clinical care without intervention

This is an observational real-world cohort study of patients presenting to fever clinics. Individual participant data (IPD) will not be shared because the dataset contains sensitive personal health information, including demographics, clinical findings, and follow-up details. Data privacy and confidentiality will be strictly maintained in accordance with institutional and ethical guidelines.