Laboratory confirmation during a large cross-border outbreak of Iatrogenic Botulism in Europe in 2023

Iatrogenic botulism is an adverse event after the injection of botulinum neurotoxin (BoNT) for medical or cosmetic purposes and is usually characterized by mild symptoms frequently involving the muscles adjacent to the injection site. The German national Consultant Laboratory for BoNT-producing Clostridia (Botulism, Tetanus) at the Robert Koch Institute was involved in the investigation of a highly unusual outbreak of travel-associated iatrogenic botulism: 30 out of 33 patients from Germany known to have received intra-gastric injection of BoNT/A for weight reduction in Istanbul (Turkey) developed symptoms of botulism, some of them were admitted to the ICU. The low concentration of BoNT in iatrogenic botulism usually prevents laboratory confirmation in human serum using standard assays (e.g., mouse bioassay). Indeed, state-of-the-art diagnostics of botulism is generally challenging due to the high molecular variability within the BoNT family, its limited time window for detection in serum and the ultimate sensitivity needed. We applied i) an Endopep-MS assay and ii) an Endopep-suspension immunoassay based on neoepitope-specific monoclonal antibodies recognizing the cleavage site in comparison to the classical mouse bioassay. While the mouse bioassay failed to detected any remaining BoNT/A we succeeded in the detection of BoNT/A with both the Endopep-MS and the Endopep-suspension immunoassay. The lessons-learned for botulism diagnostics in this largest outbreak of iatrogenic botulism ever noted will be discussed.