Sudden fever in infants may be related to various systemic inflammatory infections and immunologic diseases. 1. Inflammatory infections: respiratory infections such as bronchitis, tonsillitis, etc., can be accompanied by coughing, sneezing, runny nose and other symptoms; digestive infections, such as rotavirus, Escherichia coli enteritis, vomiting, abdominal pain, mucus, pus, blood, dilute watery or egg drop soup-like stools; urinary tract infections, there can be a decrease in urine output, urinary frequency, urinary urgency and other symptoms. 2. Immune diseases: such as Kawasaki disease, a systemic vasculitis, manifested by high fever, bulbar conjunctival congestion, chapped lips, strawberry tongue, enlarged lymph nodes, coronary artery damage and so on, for which antibiotic treatment is ineffective. Sudden fever in infants may have other causes, such as tumors, blood system diseases. It is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, give targeted treatment or treatment.