INTRODUCTION
Influenza causes epidemics worldwide every winter and is associated with mortality and morbidity. Influenza presents a wide range of clinical findings from self-limited upper respiratory tract infection to life-threatening illness that includes respiratory failure, encephalopathy, and so on. Influenza-related deaths in Japan are estimated to 3000-10000 every year, and excess death in the elderly is an especially serious problem 1. Additionally, the emergence of a novel influenza virus following the 2019 H1N1 pandemic was deeply concerning.
Treatment guidelines for adults with novel influenza were published by the Japanese Ministry of Health, Labour and Welfare in 2014 2. However, in the process of making these guidelines, it was revealed that evidence about clinical manifestation was lacking for severely ill patients with influenza. Thus, the Japanese Respiratory Society (JRS) decided to gather detailed information about severely ill patients with influenza who required hospitalization, with the goal of acquiring evidence that might improve subsequent medical care for influenza cases. The present study, which was the result of that decision, was a multicenter, prospective observational study, for which we built an internet-surveillance system to gather and analyze data from members of the JRS. From the beginning, several core institutions participated in this surveillance as a pilot study. We show the results from 5 consecutive influenza seasons.
METHODS