Regressive fever is an acute infectious disease caused by insect-borne spirochetes, characterized by periodic high fever with generalized pain, hepatosplenomegaly and bleeding tendency, and jaundice in severe cases. Depending on the vector, the disease can be divided into two types: louse-borne regressive fever (epidemic regressive fever) and tick-borne regressive fever (endemic regressive fever). The disease must be distinguished from typhus, typhoid fever, influenza, leptospirosis, epidemic hemorrhagic fever, septicemia, etc. before the appearance of the regressive fever type. 1, typhoid fever is an acute intestinal infectious disease caused by S. typhi, with persistent bacteremia and toxemia, proliferative reaction of the mononuclear phagocyte system, proliferation, swelling, necrosis and ulcer formation mainly in the lymphoid tissue of the lower ileum as the basic pathological features, typical clinical manifestations include persistent high fever, systemic toxic symptoms and gastrointestinal symptoms, relatively slow pulse, roseola, hepatosplenomegaly, leukopenia. The disease is also known as intestinal fever. However, the clinical manifestations of this disease are mainly due to the dissemination of the pathogen through the blood to the whole body organs, not caused by local lesions in the intestine, intestinal bleeding, intestinal perforation is the most important serious complications that may occur. Influenza is an acute respiratory infection caused by influenza virus, the pathogen is influenza A, B, C virus, spread by droplet, clinically there is an acute high fever, malaise, generalized muscle pain and mild respiratory symptoms, the course of the disease is short, self-limiting, middle-aged people and patients with chronic respiratory disease or heart disease is easy to complicate pneumonia, influenza in the epidemiology of the most significant features: sudden outbreak, rapid spread, widespread. The most significant epidemiological features of influenza are: sudden outbreak, rapid spread, wide spread, with a certain degree of seasonality (epidemics in northern China generally occur in the winter, while the south occurs more in the summer and winter). 3, leptospirosis is an acute systemic infectious disease caused by various types of pathogenic leptospirosis, a natural epidemic disease, rodents and pigs are the two main sources of infection. The clinical features are rapid onset, high fever, generalized aches and pains, weakness, conjunctival congestion, gastrocnemius muscle induration, superficial lymph node enlargement and other leptospirosis symptoms in the early stage; in the middle stage, it may be accompanied by pulmonary hemorrhage, diffuse pulmonary hemorrhage, myocarditis, hemolytic anemia, jaundice, generalized hemorrhagic tendency, nephritis, meningitis, respiratory failure, heart failure and other target organ damage manifestations; in the late stage, most cases recover, and a few cases may Posterior fever, ocular uveitis, and cerebral artery occlusive inflammation, which are mostly related to post-infection metaplasia, occur. Diffuse pulmonary hemorrhage, myocarditis, hemolytic anemia, etc. and liver and kidney failure are common causes of death. 4.Epidemic hemorrhagic fever is a natural epidemic disease caused by a virus. 1982 World Health Organization (WHO) named the renal syndrome hemorrhagic fever, the main pathological changes of the disease is widespread damage to small blood vessels and capillaries throughout the body, clinically characterized by fever, hypotension, bleeding, kidney damage, etc.. 5.Sepsis is a serious systemic infection caused by bacteria entering the blood circulation, growing and reproducing in it, and producing toxins. Clinical manifestations are fever, severe toxemia symptoms, rash petechiae, hepatosplenomegaly and increased white blood cell count. It is divided into Gram-positive coccus sepsis, Gram-negative bacillus sepsis and septic sepsis. Antibiotic therapy is the main treatment, supplemented by other treatments. Preventive measures are to avoid damage to the skin mucosa and to prevent bacterial infection.