1.Introduction
Influenza is a contagious respiratory disease that is widespread across the globe. Despite advances in medical technology, influenza causes considerable hospitalizations and mortality1,2. H1N1 is a subtype of influenza A virus that leads to respiratory infections and has caused two pandemics over the past 102 years3,4. The most recent pandemic of H1N1 influenza occurred in 2009 and affected 60.8 million people, resulting in 284,000 deaths worldwide5,6.
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has now spread to most countries, with WHO declaring a COVID-19 pandemic on March 1, 20207. As of June 24, 2020, more than nine million confirmed cases and 473,061 deaths had been reported globally8. The outbreak of COVID-19 began in December 2019, which also corresponded with the flu season in China and the United States9,10, the management of the disease was often complicated by the diversity in “influenza-like” clinical manifestations. Hence, differentiating the clinical impact of SARS-CoV-2 and H1N1 virus-infection will facilitate rational arrangements for implementation of COVID-19 prevention and treatment strategies. Previous studies have only compared the general epidemiological and clinical presentation of patients infected SARS-CoV-2 and H1N1 virus11-16. However, few studies have been performed to compare the severity and clinical outcome of these two types of infection.
Recently, influenza A(H1N1)pdm09 was reported as a common co-pathogen in COVID-19 patients17, and the viral co-infection is proved to be associated with more adverse clinical outcomes18-20. The data on the clinical characteristics and outcomes of patients mix-infected with SARS-CoV-2 and H1N1 are scarce, but are of paramount importance to the development of efficacious interventions and protective measures. Therefore, to facilitate efforts, both in China and globally, we report the clinical features, severity and outcome of patients with laboratory-confirmed H1N1, SAR-CoV-2 infection and co-infection with both viruses.