[Periodicity and seasonal variations in the incidence of rheumatism and their relation to various exogenous biorhythms].

The nature of the relationship between rheumatic fever morbidity on some islands in the Estonian SSR and certain heliogeophysical factors was studied over the 25-year period (1958-1983). Altogether 923 patients with rheumatic fever at the active stage were followed up. Periodicity of an increase (every 5-6 yrs) in the number of patients with active rheumatic fever was noted.