noun
incidence rate
Medical term for the rate at which new cases of a disease occur in a population over a given period.
この地域のインフルエンザ発症率は年々低下している。
The influenza incidence rate in this region has been declining year by year.
有病率 refers to prevalence (total cases at a point in time), while 発症率 refers to incidence (new cases over a period).
Compound of 発症 (onset of a disease) + 率 (rate).