the period during which premonitory symptoms of a disease or condition appear. In the prodromal period of infections, the symptoms may be nonspecific, such as weakness, headache, and mild fever, or specific, for example, the spots on the buccal mucosa in measles (the Bel’skii-Filatov-Koplik symptom, or Koplik’s spots); laboratory test results reveal changes in the body. The prodromal period is preceded by the incubation period, during which there are no symptoms despite the infection. It is followed by a period of a developed clinical picture of the disease.

The prodromal period may also be observed in some noninfectious diseases. Thus, in the period preceding myocardial infarction, an increase in the frequency and severity of attacks of angina pectoris is observed, and changes in the cellular composition of the bone marrow are observed before the onset of leukemia.