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