A new human opisthorchiasis outbreak in central Italy: a never-ending story

Opisthorchis felineus is a trematode causing a foodborne infection transmitted by raw freshwater fish belonging to Cyprinidae family. Human outbreaks in Italy dated back to 2003-2011 and involved lakes of Central Italy. The aim of this study is to report epidemiological and clinical characteristics of the human opisthorchiasis outbreak occurred in Central Italy in 2022 comparing it with previous events.

We report cases diagnosed from June to December 2022 in Perugia hospital thanks to serological and molecular tests and direct examination of feces.

Sixty-seven individuals were traced back by epidemiological investigation. Forty-seven received a diagnosis of opisthorchiasis, of which 45 were confirmed cases and two were considered as probable cases. These 47 individuals attended a Trasimeno lakeshore restaurant in May 2022. All but 20 presented symptoms, mostly fever. Sixteen (15 confirmed and 1 probable) cases required hospitalization. Feces examination revealed Opisthorchis spp. eggs in 35/45 (78%) confirmed cases. Thirty individuals underwent to serology and molecular stool test: 5 (16.7%) results positive to the former, 1 (3.3%) to the latter while 4 (13.3%) to both. Laboratory tests, available in 28 patients, showed eosinophilia in 82.1%, increase of alanine aminotransferase, gamma-glutamyl transferase and alkaline phosphatase in 64.3%, 75% and 67.9%, respectively. Because of pharmacy shortage of praziquantel, 22 patients were treated with albendazole, of which 13 failed clearing the parasite.

Opisthorchiasis still represents a challenging diagnosis, in particular for asymptomatic patients. Albendazole may lead to treatment failure. Control measures in known endemic areas should be implemented.

number 27,498/23/ON, approved by Ethical Committee of Umbrian Region in 09.13.2023.