A Cluster of Suspected Domestically Acquired Fascioliasis Among Foreign-born Residents in Hiroshima, Japan.

BACKGROUND: Fascioliasis is extremely rare in Japan and has traditionally been reported as a sporadic infection in the Japanese population. We encountered a cluster of foreign-born residents with suspected domestically acquired fascioliasis. METHODS: We retrospectively reviewed the demographics, infection routes, and clinical characteristics of consecutive patients with fascioliasis at a referral center between 2019 and 2025. RESULTS: Ten patients were identified and clustered into 2022 (n=4) and 2024 (n=6) groups. The median patient age was 30 years. All participants were foreign-born (Vietnam, n=8; Myanmar, n=1; and Thailand, n=1). Only one case was considered to have been imported, whereas nine cases were suspected to have been domestically acquired, including eight cases without recent travel. In addition to typical abdominal symptoms, pulmonary involvement was frequent; 60% had peripheral ground-glass opacities and 30% had pleural effusion on chest computed tomography. Nine patients received triclabendazole, and all recovered. Although a definitive source of infection was not identified, all patients habitually consumed raw vegetables, including those specific to Vietnamese cuisine. Most vegetables purchased from Vietnamese grocery stores were likely produced domestically. CONCLUSIONS: This cluster highlights a notable epidemiological feature of suspected autochthonous fascioliasis among foreign-born residents in Japan. Awareness of fascioliasis, including its pulmonary involvement, is required in this population.