The evolution of an epidemic: age-period-cohort modelling of mesothelioma in Casale Monferrato, 1990-2021, with projections to 2042.

backgroundIn Italy, the area of Casale Monferrato in the Piedmont Region has experienced a high burden of malignant mesothelioma (MM) due to environmental contamination from Eternit, the country's largest asbestos-cement plant, which operated from 1907 to 1986. The severity of the health impact led to the area's designation as a Site of National Interest (SIN) for environmental and health concerns. Despite the 1992 asbestos ban, the MM epidemic persists, driven by the disease's long latency. Using data from the Piedmont Malignant Mesothelioma Registry (RMM), we describe MM trends in Casale Monferrato's SIN from 1990 to 2021 and project future incidence through 2042 using Age-Period-Cohort (APC) models.

methodsIncidence rates (1990-2021) were estimated as smooth functions of age and calendar time using APC models with restricted cubic splines. Projections through 2042 were made using three approaches: (1) spline-unrestricted, (2) spline-restricted, and (3) constraint-based approach. Performance was evaluated by predicting 2010-2021 rates using data up to 2010 and comparing predicted to observed cases. Sensitivity to the number and position of spline knots was assessed.

resultsBetween 1990 and 2021, 1,282 pleural MM cases (731 men, 551 women) aged 35-96 were recorded in the Casale Monferrato SIN. Occupational exposure was reported in 61% of men and 21% of women. Non-occupational exposures, including environmental and familial exposures, were common in women (58%) than in men (22%). Incidence increased with age up to 85-90 years, and with birth cohort up to 1945 (154 and 105 per 100,000 in men and women, respectively), then declined. Rates increased over time by period until the mid-2010s and began to decrease thereafter. All approaches projected a slow but steady decline, with case numbers by 2035 returning to early 1990s levels. By 2042, incidence is estimated at 31 per 100,000 in men (8 cases) and 34 per 100,000 in women (9 cases).

conclusionsThe three approaches yielded consistent results, predicting extinction of the MM epidemic curve around mid-century. However, the health burden will persist over the next two decades, highlighting the need for sustained environmental health surveillance.