Nationwide epidemiology of hospitalized schistosomiasis in Japan: Coexistence of residual Schistosoma japonicum and non-japonicum infections

Schistosomiasis remains a global public health concern, and although transmission of Schistosoma japonicum was eliminated in Japan in 1977, patients continue to be encountered as chronic sequelae of past infections and as imported infections acquired overseas. However, nationwide data on hospitalized patients are limited. We conducted a nationwide retrospective study using the Japanese Diagnosis Procedure Combination inpatient database to clarify the contemporary epidemiological and clinical characteristics of hospitalized patients with schistosomiasis between fiscal years 2014 and 2020. A total of 111 unique hospitalized patients were identified, of whom 103 (93%) had S. japonicum infection and 8 (7%) had non-japonicum schistosomiasis. Patients with S. japonicum infection were older than those with non-japonicum infection (mean age 77.4 vs. 43.8 years), and the age distribution showed a predominant peak in elderly individuals, with a smaller relative increase among middle-aged adults. Coexisting hepatobiliary conditions among S. japonicum cases, including liver cirrhosis (25%) and hepatocellular carcinoma (14%), and colorectal cancer was identified in 4% of patients. Geographic clustering was evident in historically endemic regions, particularly Yamanashi and Fukuoka Prefectures. In contrast, non-japonicum cases were sporadic and more frequently observed in younger individuals. Praziquantel was administered to 4 patients (4%), consistent with the predominance of chronic sequelae rather than active infection. In conclusion, the current inpatient burden of schistosomiasis in Japan predominantly reflects the long-term clinical legacy of past S. japonicum transmission, underscoring the importance of continued clinical awareness and surveillance despite the elimination of domestic transmission.