Influenza

Influenza (flu) is an acute respiratory infectious disease caused by influenza viruses, with pathogens being type A, B, and C influenza viruses, transmitted through droplets. Clinically, it presents with sudden high fever, fatigue, generalized muscle aches, and mild respiratory symptoms, with a short course and self-limiting nature. Middle-aged individuals and patients with chronic respiratory diseases or heart disease are prone to complicating pneumonia. The most notable epidemiological feature of influenza is: sudden outbreak, rapid spread, wide geographic involvement, and a certain seasonality (in northern China, epidemics generally occur in winter, while in southern China, they mostly occur in summer and winter).