# Epidemiology of Kudoa septempunctata food poisoning in Japan from 2013 to 2023

## TL;DR

This study tracks Kudoa septempunctata food poisoning cases in Japan from 2013 to 2023, showing trends in outbreaks linked to raw flounder consumption.

## Contribution

The study provides the first national-scale epidemiological analysis of K. septempunctata food poisoning in Japan over a 10-year period.

## Key findings

- Reported cases peaked in 2014 (429 cases) and dropped during the COVID-19 pandemic.
- Flounder-based sashimi and sushi were responsible for 99% of cases.
- Yamaguchi, Osaka, and Fukuoka prefectures had the highest number of cases.

## Abstract

Kudoa septempunctata, a parasite found in olive flounder, poses a growing food safety risk in East Asia, particularly in Japan and South Korea. K. septempunctata poisoning caused by raw fish consumption causes brief gastrointestinal symptoms. However, long-term, national-scale aggregated epidemiological data for K. septempunctata food poisoning are limited. In this retrospective study, we examined the recent epidemiological trends and characteristics of K. septempunctata food poisoning cases reported in Japan between January 2013 and December 2023. Ministry of Health “Foodborne Illness Statistical Data” were assessed for case counts, outbreaks, and implicated foods. Reported cases totaled 2009, reaching a peak in 2014 (429 cases) then declining to < 100 cases during the COVID-19 pandemic. October had the highest number of monthly reports. Flounder, particularly sashimi and sushi, were implicated in 99% of cases. The highest case counts occurred in Yamaguchi, Osaka, and Fukuoka prefectures (160, 155, and 154, respectively). Tottori, Shimane, Yamaguchi and Oita prefectures had the highest incidence rates (14.3, 10.9, 10.7, and 10.7 per 1,000,000 population, respectively). Prefectures along the Sea of Japan typically reported higher incidence rates. This study highlights the importance of continued surveillance and reporting of K. septempunctata poisoning, and the need to consider Kudoa infections in the differential diagnosis of food poisoning cases involving raw fish consumption.

The online version contains supplementary material available at 10.1038/s41598-026-38632-2.