Pickled eggs linked to Chinese botulism cases

Five people fell sick in China recently after eating pickled eggs contaminated with Clostridium botulinum.

In July 2024, two people with suspected foodborne botulism went to the emergency department of a hospital in Shandong Province. The patients had consumed homemade pickled eggs. The Huancui District CDC and Weihai CDC initiated epidemiological investigations.

According to the study published in China CDC Weekly, from July 16 to 17, the hospital admitted three other patients with the same food exposure history and symptoms.

The five patients had similar symptoms, including blurred vision and drooping of the upper eyelid as the primary symptoms, accompanied by difficulties swallowing, speaking, and breathing.

Epidemiological investigations revealed one of the patients prepared pickled eggs using home-raised chicken eggs in late June. The eggs, laid by free-range hens in the village, were washed, boiled, cooled, and brined with edible salt at room temperature for two weeks.

Their surfaces may have been contaminated by Clostridium botulinum from soil or livestock feces. Inadequate cleaning before pickling and the anaerobic conditions produced during the pickling process likely led to botulinum toxin production, said scientists. 

Positive patient and food samples
From July 12 to 14, portions of the pickled eggs were given to the second patient’s son and daughter-in-law, who shared them with colleagues. A total of eight individuals consumed the pickled eggs without heating and developed varying degrees of symptoms. Botulinum toxin can be destroyed by heating at 80 degrees C (176 degrees F) for 30 minutes or 100 degrees C (212 degrees F) for 10 to 20 minutes. 

A patient’s fecal samples and pickled eggs tested positive for Clostridium botulinum type A.

On July 17, the hospital administered botulinum antitoxin treatment. By July 18, three patients were being treated in the Emergency Intensive Care Unit of the hospital. Two other patients had mild symptoms. No deaths were reported.

The Huancui District CDC collected 10 environmental samples from the kitchen and refrigerator of the patient who prepared the eggs. These samples included smears of raw eggs, kitchen utensils used for storing and cleaning pickled eggs, and swabs from the refrigerator and trash bin.

A dozen strains of Clostridium botulinum were isolated from the pickled eggs, rectal swabs/feces of patients, and environmental specimens. A mouse bioassay showed that seven enrichment cultures contained botulinum neurotoxin type A.

“This outbreak indicated that foodborne botulism remains a public health issue in China. We need to strengthen publicity and education efforts to inform people of the potential risk of botulism associated with consuming homemade traditional pickled foods. Heating and boiling homemade foods thoroughly can destroy toxins and prevent foodborne botulism,” said researchers. 

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