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We analyzed 2015–2024 national surveillance data on Kudoa septempunctata parasite–associated foodborne disease in South Korea. Monthly cases decreased 95% during the COVID-19 pandemic, with no significant recovery through 2024; affected municipalities dropped from 89 to 27. Our findings are consistent with restaurant-based raw fish consumption as the principal transmission pathway.
Kudoa septempunctata is a myxosporean parasite that causes transient gastroenteritis within hours of consuming raw infected fish ( 1 ). Although best known from farmed olive flounder ( Paralichthys olivaceus ), it has been reported from phylogenetically diverse marine fishes, including members of the order Tetraodontiformes (black scraper [ Thamnaconus modestus ], wild grass puffer [ Takifugu alboplumbeus ]) and the series Eupercaria (Japanese whiting [ Sillago japonica ]), indicating that human exposure is not limited to olive flounder ( 2 ). After the K. septempunctata parasite was identified in Japan in 2011 ( 1 ), South Korea, the world’s largest producer of farmed olive flounder, designated it a notifiable foodborne pathogen in 2015. However, national surveillance during the COVID-19 pandemic has not been analyzed. We examined whether pandemic-related restrictions on dining out interrupted K. septempunctata parasite incidence and whether a rebound followed restoration of normal dining behaviors, thereby assessing whether restaurant-based exposure is the dominant transmission pathway.
We obtained monthly outbreak and case data for 2015–2024 from the Ministry of Food and Drug Safety surveillance system, aggregated by municipality (si-gun-gu, which consists of cities, counties, and districts; n = 229) and linked to Statistics Korea population data. Using February 2020 as the intervention point, we fitted a negative binomial interrupted time series model with a population offset and Fourier seasonality terms (K = 2). We compared municipality-level choropleth maps of crude incidence rates and Getis–Ord statistic hotspots between the pre–COVID-19 (2015–2019) and COVID-19/postpandemic (2020–2024) periods ( Appendix Figure 1).
During 2015–2024, a total of 1,230 cases and 215 K. septempunctata outbreaks were reported ( Table ). Prepandemic, annual cases nearly tripled from 114 in 2015 to 308 in 2019, and outbreaks increased from 15 to 48. Restaurants accounted for 167 (77.7%) of all outbreaks, and no household outbreak was reported in any year, implicating commercial food-service venues as the dominant exposure setting ( 3 ). Cases dropped abruptly to 40 in 2020 and 8 in 2021, then increased gradually to 70 in 2024.
Figure . Interrupted time series analysis of monthly Kudoa septempunctata parasite–associated foodborne disease cases, South Korea, January 2015–December 2024. Blue line, observed monthly counts; red line, model-fitted trend with seasonality removed;...
The interrupted time series analysis ( Figure ) showed a highly significant reduction at COVID-19 onset (β 2 = −2.948 [95% CI, −3.919 to −1.989]; p<0.001), corresponding to a 95% drop in monthly cases. The postpandemic…