Foodborne Illness-Related Diagnostic Coding and Healthcare-Utilization Patterns in South Korea, 2023: A Nationwide Claims-Based Descriptive Study

Background: Foodborne illness surveillance commonly focuses on reported outbreaks and laboratory-confirmed infections. Nationwide information on foodborne illness-related diagnoses recorded during routine healthcare encounters remains limited in South Korea. This study described the volume and distribution of claims-defined foodborne illness-related episodes and associated diagnostic category records documented in the 2023 HIRA database. Methods: This nationwide retrospective descriptive study used administrative reimbursement claims data from the Health Insurance Review and Assessment Service in 2023. Repeated qualifying encounters for the same patient were grouped into episodes using a 30-day gap rule. For the monthly analysis, each episode was counted once and assigned to the diagnostic category first recorded during the episode; other category-specific analyses used non-mutually exclusive diagnostic category records. Unique episodes were summarized by calendar month, whereas diagnostic category records were summarized by demographic characteristics, selected underlying diseases, healthcare institution type, and region. Results: A total of 6,829,577 unique claims-defined episodes generated 7,754,215 diagnostic category records because an episode could contribute to more than one diagnostic category. Unspecified records accounted for 79.3%, followed by bacterial records (12.1%), viral records (8.6%), and protozoal/other-cause records (<0.1%). Viral and unspecified records were more frequently observed in younger age groups, whereas bacterial records were concentrated among adults aged 19–64 years. Most records were associated with clinic visits (80.3%). Monthly episode counts showed variation, with the highest count observed in July and relatively high counts also observed in January, August, and September. Crude record rates based on healthcare institution location varied across regions. Conclusions: Foodborne illness-related diagnostic records were predominantly unspecified and were most frequently documented in clinics, suggesting limited etiologic specificity in routine diagnostic coding. Claims-based findings may complement existing surveillance but should not be interpreted as confirmed disease incidence or etiologic distribution.