Criminal Attribution in Suspected Foodborne Listeriosis: A Methodological Template for Pathogen-Specific Forensic Investigation

Background: Listeria monocytogenes is an ubiquitous foodborne pathogen capable of persisting in food-processing environments, domestic settings, and water systems; consequently, the mere co-detection of the microorganism in a patient and in a food product is insufficient to support criminal causation. In judicial proceedings, attribution of invasive listeriosis to a specific food and food business operator requires a pathogen-specific evidentiary chain that exceeds the standards used for public health surveillance. Methods: We performed a retrospective medico-legal and methodological analysis of a fatal listeriosis case that triggered criminal prosecution for foodborne homicide, systematically assessing the investigative chain according to temporal plausibility, food traceability, compliance with European and ISO microbiological standards, interpretation of whole-genome sequencing (WGS) data for an ubiquitous pathogen, and clinical causation of death. Results: The analysis identified critical weaknesses in the accusatory reconstruction, including incompatibility with established incubation periods, lack of proof that the sampled food lot corresponded to the product actually consumed, deviations from standard microbiological procedures, reliance on a poorly documented “clinical” isolate for WGS, non-specific genomic findings within a widely disseminated clonal complex, and the presence of plausible alternative environmental reservoirs. Clinically, the immediate cause of death was more consistent with hypovolemic shock due to uncontrolled gastrointestinal bleeding than with ongoing listerial sepsis. Conclusions: This article demonstrates how, in cases involving ubiquitous pathogens, failure to adopt a pathogen-specific investigative and interpretative framework may lead to methodologically fragile criminal allegations, potentially increasing litigation burden and costs for the justice system. A methodologically robust approach integrating microbiology, genomics, epidemiology and medico-legal causation analysis is essential for fair and scientifically sound criminal proceedings.