2.1 Study population
This retrospective study analyzed patients admitted to the Guangzhou Eight People’s Hospital with laboratory-confirmed H1N1 and COVID-19 infection. After excluding 7 patients who were minors (≤18 years) and four patients with immune deficiency, a total of 220 H1N1-infected patients between January 2016 and May 2019 were enrolled in this study. For patients with COVID-19, we excluded 6 patients who were minors (≤18 years) and three patients with immune deficiency, after which 285 COVID-19 patients admitted to the hospital between January 2020 and April 2020 were enrolled. Of these patients, 36 patients who had a mixed infection of H1N1 and COVID-19 were used as the comparator group. The study was approved by the Guangzhou Eight People’s Hospital Medical Ethical Committee.