If a child has a low fever of 37.4 degrees, if it is accompanied by nasal congestion, runny nose and sore throat, it is likely that the fever is caused by a chronic infection of the respiratory system. In this case, the blood test may show an increase or decrease in white blood cells, which may be caused by bacterial infection or viral infection. If you have a cough, night sweats, or a low fever in the afternoon, you cannot rule out a low fever caused by Mycobacterium tuberculosis, and you need a chest X-ray and a tuberculin test. If the fever is 37.4 degrees due to Mycobacterium tuberculosis, specific anti-tuberculosis treatment is needed and a specialized tuberculosis hospital is required. In addition, rare diseases, such as malignant tumors, hematologic diseases or rheumatic immune system diseases, may also cause a child to have a low fever and require a specific examination at a hospital to confirm the diagnosis.