The danger period of hemorrhagic fever cannot be judged simply, and it is impossible to state the exact number of days. Generally, it has to be judged according to the type of infected virus, the patient’s own condition, etc., and some patients may have long-term sequelae even if they are cured. Two main clinical syndromes occur after human infection with hantaviruses: hemorrhagic fever with renal syndrome (HFRS) caused by hantaviruses, Seoul, Pumara and Dobrava viruses, and hantavirus cardiopulmonary syndrome (HCPS). A German study showed that blood in the urine occurs in most patients after the acute phase of Puumala virus infection, possibly suggesting persistent glomerular cell damage, and that patients recovering from HFRS may have a higher incidence of lymphoma. Puumala virus infection often involves the lymphatic system, and splenomegaly is present in almost all patients during the acute phase of viral infection. Hemorrhagic fever is extremely dangerous. When patients present with symptoms such as fever and bleeding, they should seek prompt medical attention and have blood tests, urine tests and electrocardiograms done as soon as possible to further understand their condition and make a clear diagnosis.