BACKGROUND: Since the outbreak of Coronavirus Disease 2019 (COVID-19) in China in December 2019, considerable attention has been focused on its elucidation. However, it is also important for clinicians and epidemiologists to differentiate COVID-19 from other respiratory infectious diseases, such as influenza viruses. RESEARCH QUESTION: The aim of the study was to explore the different clinical presentations between COVID-19 and influenza A (H1N1) pneumonia in patients with acute respiratory distress syndrome (ARDS). STUDY DESIGN: and Methods: This was a retrospective case-control study. We compared two independent cohorts of ARDS patients infected with either COVID-19 (n=73) or H1N1 (n=75). We analyzed and compared their clinical manifestations, imaging characteristics, treatments, and prognosis. RESULTS: The median age of COVID-19 patients was higher than that of H1N1 patients, and there was a higher proportion of males among COVID-19 patients (p<0.05). COVID-19 patients exhibited higher proportions of non-productive coughs, fatigue, and gastrointestinal symptoms than those of H1N1 patients (p<0.05). H1N1 patients had higher sequential organ failure assessment (SOFA) scores than COVID-19 patients (p<0.05). The PaO2/FiO2 of 198.2 mmHg in COVID-19 patients was significantly higher than the PaO2/FiO2 of 107.0 mmHg of H1N1 patients (p<0.001). Ground-glass opacities was more common in COVID-19 patients than in H1N1 patients (p<0.001). There was a greater variety of antiviral therapies administered to COVID-19 patients than to H1N1 patients. The in-hospital mortality of COVID-19 patients was 28.8%, while that of H1N1 patients was 34.7% (p=0.483). SOFA-score adjusted mortality of H1N1 patients was significantly higher than that of COVID-19 patients with the rate ratio was 2.009 (95% CI [1.563, 2.583], p<0.001). INTERPRETATION: There were many differences between COVID-19 and H1N1-induced ARDS patients in clinical presentations. Compared with H1N1, patients with COVID-19 induced ARDS had lower severity of illness scores at presentation and lower SOFA-score adjusted mortality.
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