Viral particles can be seen by electron microscopy in the acute phase, and specific IgM antibodies in the serum are detected in the acute phase or early recovery. Specific viral DNA can be detected in serum and throat secretions. 1. Need to be distinguished from rubella and measles. 2, need to be distinguished from skin, vascular damage diseases. (1) Vascular purpura (vascular purpura) Patients are both pediatric and adult. First appear fever, sore throat, runny nose, etc., and 48h later appear rash, which is characterized as vascular purpura. It appears first on the extremities and later extends to the trunk, neck and even the face. The purpura lasts for several days and may be accompanied by short-term leukocytopenia and thrombocytopenia. Some patients have abdominal pain or large joint pain. The histological examination has both necrotizing vasculitis and non-necrotizing vasculitis manifestations. (2) erythema infectiosum This disease is also known as the fifth disease, which was described in detail by Tschamer in 1889. It has been described in detail by Tschamer in 1889. There were several epidemics around the world until 1981, when HPV-B19 was identified as the cause. The clinical manifestation of infectious erythema in children starts with fever, general malaise, sore throat, runny nose, etc. After 2 to 3 days, a rash appears, mostly starting on the face, which soon fuses into patches and is accompanied by mild edema, forming a special “palm face”. The rash soon extends to the trunk and extremities. The rash starts as a maculopapular rash and then fades to a reticular or lace-like pattern in the middle. The rash may be aggravated by sun exposure, exercise, and bathing, and is accompanied by pruritus. The rash lasts 2 to 4 days and the pigmentation may fade after a few days, with the full course of the disease lasting 5 to 9 days. There are a few adults with HPV-B19 infection who show infectious erythema, but they rarely have a “slap face” and the rash is also less frequent. However, a few days to a few weeks after the disease, 80% of people develop arthralgia. (3) Scarlet fever This disease is acute in appearance, with clinical manifestations such as sore throat, high fever, diffuse erythema, pale circles around the mouth, strawberry tongue, and peeling skin after healing. Papanicolaou’s sign: positive. (4) Rubella Upper respiratory tract khat symptoms are more pronounced, fever, measles-like rash, swollen lymph nodes behind the ear and occiput. (5) Measles High fever, marked upper respiratory cicatricial symptoms, maculopapular rash with normal skin between the rashes. Early buccal mucosa can be seen as Koplik’s spots.