RESUMEN
Leprosy is a chronic infectious disease caused by Mycobacterium leprae. Massive internal migration from rural to urban areas poses new challenges for leprosy control in Shanghai, China. This retrospective epidemiological study examined new cases of leprosy diagnosed in Shanghai from 2000 to 2019, with emphasis on internal migration cases. There were 145 cases of leprosy in the study period; the majority of cases (89.0%) were internal migrants. Migrant cases had a mean of 25.4 months lag time from onset of symptoms to diagnosis, which was significantly longer than that of resident cases (mean 10.8 months, p < 0.001). Greater lag time from the first visit to diagnosis was observed in migrant cases (mean 23.2 months) compared with resident cases (mean 9.4 months, p < 0.001). A large majority of cases (91.0%) had been misdiagnosed. Internal migrant cases were responsible for most incidences of leprosy in Shanghai. They often did not receive timely diagnosis and treatment, which may have an adverse impact on the prevention of epidemic leprosy.