Only fever without other symptoms is considered to be a possible early manifestation of the disease, and other symptoms have not yet been revealed. Fever can be caused by infectious factors, non-infectious factors, and other factors. 1. Infectious factors: for example, bacterial infections, viral infections or certain fungal infections, as well as other microbial infections, may lead to fever, including chlamydia and mycoplasma infections, which may be manifested in the early stage of the disease only as a symptom of fever. 2. Non-infectious factors: Secondly, there may also be non-infectious fevers, such as rheumatic fever, serum sickness, drug fever, tumors, etc., which may have fever as the first symptom. If the fever persists for a long time, it is recommended to go to the hospital as soon as possible to clarify the cause of the disease, so as not to delay the disease.