Researchers have detailed an outbreak that sickened 67 people in Italy in 2022 caused by a parasite after people ate fish in a restaurant.
Opisthorchis felineus is a trematode causing a foodborne infection transmitted by eating raw or partially cooked infected freshwater fish.
An opisthorchiasis outbreak occurred in May 2022 in the Umbria region of central Italy. 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 probable infections.
According to the study published in the Springer Nature journal Infection, of the 47 cases, 22 were males, with a mean age of over 45, and 41 were Umbria region residents.
These 47 people attended a Trasimeno lakeshore restaurant in May 2022. All but 20 presented symptoms, mostly fever. Sixteen cases required hospitalization. Feces examination revealed Opisthorchis eggs in 35 of 45 confirmed cases.
Patients ate marinated filets at a restaurant in Sant’Arcangelo in Magione, Perugia, and were diagnosed with an Opisthorchis felineus infection from June to December 2022.
Outbreak summary
The seriousness of infection caused by Opisthorchis felineus depends on the parasitic burden, susceptibility of the host and occurrence over time of infections/reinfections causing ongoing inflammatory conditions.
Diagnosis is hampered by the lack of pathognomonic signs and symptoms and the decreasing number of health professionals with the skills needed 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 have reportedly been infected with this parasite, all living or traveling to the Latium or Umbria regions. Scientists said the recurrence of these events highlights the need to implement control measures in known endemic areas.
In June 2022, 11 index patients with fever or abdominal issues were admitted to the hospital. All of them ate a meal at the same lakeshore restaurant on several days in May 2022. The restaurant was managed by the fishermen cooperative owning the annex fish market as well.
Patients remembered eating marinated filets of Largemouth bass or common whitefish and tench pate as a starter. The high number of asymptomatic patients suggests that people ingested only a low infecting dose.
No fish sample was positive for Opisthorchis spp. metacercariae, even if the tench remained the major suspect, said researchers.
The best way of preventing opisthorchiasis is decontaminating freshwater fish by freezing it at -10 degrees C (14 degrees F) for five to 70 days or cooking until the fish core reaches 65 degrees C (149 degrees F) for at least one minute.
Of 22 patients treated with albendazole, due to a shortage of praziquantel, 13 still had Opisthorchis eggs in stool at up to six months post treatment. All of them received a second successful treatment with praziquantel.
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