Comparison of clinical characteristics and outcomes between COVID-19 pneumonia and H1N1 influenza

Introduction: The COVID-19 pandemic has been likened to the 2009 H1N1 influenza pandemic. We aim to study the similarities and differences between patients hospitalized with COVID-19 and H1N1 influenza in order to provide better care to patients, particularly during the co-circulation of Influenza A Subtype H1N1 and SARS-CoV-2. Material and methods: A retrospective cohort study was conducted in order to compare clinical characteristics, complications, and outcomes of hospitalized patients with PCR-confirmed H1N1 influenza pneumonia and COVID-19 at a tertiary care center in Karachi, Pakistan. Results: A total of 115 patients hospitalized with COVID-19 were compared with 55 patients with H1N1 Influenza A pneumonia. Median age was similar in both COVID-19 patients (54 years) and in patients with H1N1 influenza (59 years), but there was male predominance in COVID-19 patients (OR = 2.95; 95% CI: 1.12-7.79). Patients with COVID-19 pneumonia were 1.34 (95% CI: 1.14-1.62) times more likely to have a greater duration of illness prior to presentation compared to H1N1 influenza patients. COVID-19 patients were 4.59 times (95% CI: 1.32-15.94) more likely to be admitted to a general ward compared to H1N1 pneumonia patients. Moreover, patients with COVID-19 were 7.62 times (95% CI: 2.42-24.00) more likely to be treated with systemic steroids compared to patients with H1N1 pneumonia. The rate of nosocomial infections as well as mortality was similar in both H1N1 and COVID-19 pneumonia. Conclusion: Our study found a male predominance and longer duration of illness in hospitalized patients with COVID-19 compared to H1N1 influenza patients but no difference in outcomes with either infection.