Etiology Human herpesvirus type 6 (HHV-6) is the main cause, other rare causes are human herpesvirus type 7 (HHV-7), coxsackievirus A and B, echovirus, adenovirus, and parainfluenza virus. Clinical manifestations are as follows: 1. Fever: Incubation period 1-2 weeks, average 10 days. Most of the children have no prodromal symptoms but sudden onset of high fever, body temperature 39℃～40℃ or more, except for loss of appetite, the general mental state of the child has no obvious changes, but a few children have nausea, vomiting, cough, tympanic membrane inflammation, perioral swelling and hematuria, very few appear drowsy, convulsions, etc., the pharynx and tonsils are mildly congested and the head and neck, occipital lymph nodes are mildly enlarged, manifesting as high fever with mild symptoms and signs disproportionate. 2. Rash: After 3 to 5 days of fever, the fever suddenly decreases and the body temperature drops to normal within 24 hours, and the rash appears after the fever subsides. The rash usually occurs first on the face and neck and trunk, and then gradually spreads to the proximal extremities. It lasts 1 to 2 days and then subsides, leaving no trace of the rash, no flaking and no hyperpigmentation. In some children, erythema can appear on the palatal lobe in the early stage, and the rash can subside without special treatment. 3.Examination: The main basis for determining the diagnosis is the detection of serum anti-HHV-6 antibodies, and also the detection of viral DNA by viral isolation or PCR (polymerase chain reaction). on the first to second day of illness, the white blood cell count may be increased, but after the rash is reduced, while the lymphocyte count is increased, up to 90% or more. 4. Diagnosis and differential diagnosis: Infants and children under 2 years of age with sudden high fever without other systemic symptoms and a rash that appears when the fever subsides should be considered. This disease needs to be differentiated from measles, rubella and Kawasaki disease. The differentiation from rubella is more important because the rash is similar, but children with rubella do not have high fever, and the rash appears along with fever, and swollen lymph nodes behind the ear and occipital area are more pronounced. The rash is not only a fever, but also a rash that is more pronounced behind the ears and occipital lymph nodes. 5. Treatment: Patients with mild type can rest in bed, give appropriate amount of water and nutrition. In case of high fever, antipyretics and symptomatic treatment can be given. However, for infants and children with immunodeficiency or severe cases, antiviral therapy is required. Prognosis The prognosis of this disease is good and serious complications are rare. HHV-6 encephalopathy, hepatitis and hemophagocytic syndrome have been reported to occur in children.