Decline of Parkinson's disease incidence in Israel. The value of cohort analysis

BACKGROUND: The "birth cohort" effect (BCE) is the impact of the external environment on the health status of individuals born at a given time in relation to events that occurred during that timeframe. Cohort studies are used to identify the etiology of diseases and links between their risk factors. We undertook the first study to delineate the BCE in Israeli PD patients based upon big data. METHODS: We applied the US National Institutes of Health data analytic tool to perform a cohort analysis of PD data collected in the largest Israeli health services provider (Clalit Health Services) from 2002 to 2021. PD patients were divided into twelve 5-year age groups (40-44 to 95-99) for four five-year periods (2002-2006, 2007-2011, 2012-2016, and 2017-2021). The BCE was evaluated by counting the number of diagnosed patients and using cohort rate ratios (RRs) separately for male and female PD patients born between 1905-1909 and 1975-1979. The significance of the BCE was assessed by the Wald χ2 test. RESULTS: There was a peak in diagnosed PD cases between 1919 and 1949, followed by a steady decline in PD incidence rates (RRs), beginning with the 1905-1909 cohorts and continuing through the 1975-1979 cohorts in both sexes. The cohort RRs decreased from 12.94 (CI: 7.76-21.55) for females and 10.83 (CI: 7.52-15.59) for males in the 1905-09 cohorts to 0.35 (CI: 0.15-0.83) and 0.45 (CI: 0.28-0.74), respectively, in the 1975-79 cohorts. A 5-year lag in BCE was found in females compared to males. CONCLUSION: The BCE was characterized by a reduction in the incidence of Israeli PD patients, possibly reflecting epidemiological and sociodemographic changes that occurred in Israel.