Researchers have detailed an outbreak that sickened dozens of people in Italy in 2022, caused by a parasite after people ate fish at a restaurant.
Opisthorchis felineus is a trematode that causes a foodborne infection transmitted by eating raw or partially cooked infected freshwater fish.
In May 2022, an outbreak of opisthorchiasis occurred in the Umbria region of central Italy. 67 people have been traced through epidemiological research. 47 were diagnosed with opisthorchiasis, including 45 confirmed cases and two probable infections.
According to the study published in the Springer Nature journal InfectionOf the 47 cases, 22 were men, with an average age of more than 45 years, and 41 were residents of the Umbria region.
These 47 people visited a restaurant on Lake Trasimeno in May 2022. All but 20 showed symptoms, mainly fever. Sixteen cases required hospitalization. Stool examination revealed eggs of Opisthorchis in 35 of the 45 confirmed cases.
Patients ate marinated fillets at a restaurant in Sant’Arcangelo in Magione, Perugia, and were diagnosed with Opisthorchis felineus from June to December 2022.
Summary of the outbreak
The severity of infection caused by Opisthorchis felineus depends on the parasite burden, host susceptibility, and the occurrence over time of infections/reinfections causing persistent inflammatory conditions.
Diagnosis is hampered by the lack of pathognomonic signs and symptoms and the decreasing number of health professionals with the skills necessary to identify Opisthorchis eggs in stool samples. The time between infection and detection of specific IgG in serum usually ranges from three to eight weeks.
From 2003 to 2022, 259 people are reported to have been infected with this parasite, all of whom lived or traveled in the regions of Latium or Umbria. Scientists say the recurrence of these events highlights the need to implement control measures in known endemic areas.
In June 2022, 11 index patients were admitted to hospital with fever or abdominal complaints. They all ate a meal at the same lakeside restaurant on multiple days in May 2022. The restaurant was managed by the fishing cooperative that also owned the fish market in the annex.
Patients recalled eating marinated fillets of largemouth bass or common whitefish and tench steak as an appetizer. The high number of asymptomatic patients suggests that people have ingested only a low dose of infection.
No fish sample was positive for Opisthorchis spp. metacercariae, even though the tench remained the main suspect, researchers said.
The best way to prevent opisthorchiasis is to disinfect freshwater fish by freezing them at -10 degrees C (14 degrees F) for five to 70 days or by cooking them until the fish core reaches 65 degrees C (140 degrees F) for at least one minute ( reaches 149 degrees F).
Of the 22 patients treated with albendazole for praziquantel deficiency, 13 still had Opisthorchis eggs in the stool up to six months after treatment. They all received a second successful treatment with praziquantel.
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