Rare pathogen in rice behind outbreak in China

Contaminated rice was the source of an outbreak in China caused by a rare pathogen.

Bacillus paranthracis belongs to the Bacillus cereus group. However, globally reported outbreaks remain rare and the genomic characteristics of outbreak isolates are seldom characterized.

An epidemiological and genomic investigation was done to understand the cause of a foodborne outbreak in Huzhou, Zhejiang province, in July 2024, with nine patients confirmed. Results were published in the International Journal of Food Microbiology.

Ten Bacillus paranthracis isolates were identified, including four patient samples and six from food. Investigations showed that the Bacillus paranthracis isolates with sequence type 26 from uncooked rice were responsible for the outbreak. Because of the spores, heating the rice did not inactivate the pathogen.

In July 2024, several patients with acute gastroenteritis were treated at a hospital in Huzhou. These people were from different families and companies but had lunch in the same restaurant. In response, the Huzhou Center for Disease Control and Prevention conducted field epidemiological investigations and collected samples. 

Nine people sick
Officials carried out a sanitary investigation of the restaurant including taking samples from the kitchen environment, plus food and water for testing. Stool samples were taken from patrons and restaurant employees.

Nine suspected cases were recorded. All patients had nausea/vomiting, eight had diarrhea, and six reported abdominal pain. Seven of them were admitted to hospital. Following rehydration and antibiotics treatment they were discharged after their health improved.

All patients fell sick on July 18. Five were male and four were female. They ranged in age from 20 to 45. 

The investigation found that rice was steamed in advance and left to cool naturally, then reheated and sold. Also, unused ingredients such as rice and tofu from the day before were found in the refrigerator. Officials speculated there was cross-contamination of ingredients in the refrigerator.

Combining epidemiological investigation and whole genome sequencing analysis, scientists confirmed the outbreak’s source was the Bacillus paranthracis isolated from food in the restaurant.

“Our study underscores that authorities need to implement systematic surveillance for Bacillus paranthracis infections from humans, which is essential for tracking of the source of infection to ensure public health,” said researchers.

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