Investigation and analysis of a botulism outbreak caused by consumption of homemade pickled eggs

ObjectiveTo investigate a botulism outbreak caused by consumption of homemade pickled eggs in Weihai City， Shandong Province， and to provide reference for future prevention and control measures.MethodsA population-based epidemiological investigation was conducted in accordance with the Technical Guidelines for Epidemiological Investigation of Food Safety Accidents （2012 edition）. Both descriptive and analytical epidemiological methods were employed for data analysis. Botulinum toxin genes in leftover food， environmental samples， and biological specimens were detected using real-time quantitative polymerase chain reaction （qPCR）. Clostridium botulinum strains were isolated and botulinum toxin was typed with reference to GB 4789.12—2016. Furthermore， whole-genome sequencing （WGS） and phylogenetic analysis were performed on the isolates.ResultsAmong the 8 individuals exposed to the pickled eggs， 5 developed botulism， yielding an attack rate of 62.50% （5/8）. None of the unexposed individuals became ill. Retrospective cohort analysis identified the pickled egg as a risk factor （P<0.001）. The incubation period ranged from 13.5 to 67.5 hours. Predominant clinical manifestations included fatigue， blurred vision， ptosis （each 100.00%）， as well as nausea and vomiting （each 80.00%）. A total of 12 C. botulinum were isolated. All strains were positive for the type A botulinum toxin gene tested by qPCR. Mouse bioassay confirmed the presence of type A botulinum toxin in all 7 enrichment cultures. WGS analysis revealed that these isolates were closely genetically related.ConclusionThis outbreak was confirmed as a botulism outbreak caused by the consumption of homemade pickled eggs contaminated with C. botulinum producing type A botulinum toxin. It is recommended that targeted health education be carried out among high-risk regions and populations regarding the processing， storage， and consumption practices to enhance their awareness of safety precautions for such foods.