Patients admitted to the cardiology department with acute heart failure who have a nasopharyngeal respiratory virus PCR test performed within 72 hours of admission will be enrolled in the study cohort.

The detection rate of respiratory viruses including influenza virus, RSV, and coronavirus will be analysed. The investigators will also look for seasonal changes in the frequency of respiratory viruses and differences in the clinical presentation of heart failure based on respiratory virus infection.

Inclusion Criteria:

• Adult aged 19 years or older admitted to the cardiology department with acute heart failure
• NT-proBNP >300 pg/mL
• Clinician judgement of possible respiratory viral infection (fever >38 degrees or cough, respiratory symptoms such as sputum or consolidation on x-ray or CRP >5 mg/dL)
• Patients who have a nasopharyngeal swab for respiratory virus PCR test performed within 72 hours of admission for any of the 3 reasons

Exclusion Criteria:

• Patients with a clear other cause of acute heart failure (ex. ACS, bradycardia requiring a pacemaker, uncontrolled tachycardia, uncontrolled severe hypertension (SBP >180mmHg or DBP >110mmHg), haemoglobin <7g/dL or AHF precipitated by medication non-adherence)
• If the cause of pulmonary oedema is prominently attributed to exacerbation of CKD
• If there is a clear other source of infection that can explain the fever

Patients hospitalised with AHF at three healthcare facilities who had respiratory virus PCR testing performed