Epidemiological Trends and Impact of Leprosy Control Strategies in Gansu, China: A 70-Year Interrupted Time-Series Analysis (1950–2020)

Gansu in northwestern China has maintained leprosy elimination at the national and county level, yet localized transmission persists in certain endemic foci. This 70-year analysis (1950-2020) assessed the impact of key control strategies using an interrupted time-series analysis of new case detection rate (NCDR) with break points at the 1958 "survey-isolate-treat" strategy and the 1987 multidrug therapy (MDT) rollout. Among 4,872 registered cases, NCDR rose initially and then declined steadily to 0.027/100,000 by 2020. Significant geographic clustering was observed in southeastern counties (Moran's I = 0.403, P < 0.05). Most cases were male farmers (male-to-female ratio 2.37:1), and Han ethnicity accounted for 75.9% of all cases. The proportion of multibacillary cases increased significantly from 78.0% before 1987 to 84.9% after MDT implementation. Time-series analysis indicated that the 1958 strategy was associated with a sustained decline in detection rates during the high-endemic phase, whereas MDT introduction in 1987 led to an immediate level reduction during the low-endemic phase. These results underscore the complementary role of historical integrated control measures and modern chemotherapy in sustaining leprosy elimination. However, transmission persists, and the rising proportion of multibacillary cases highlights the ongoing need for targeted active surveillance, contact screening, and strengthened early detection to achieve WHO 2030 eradication targets.