China reports 80 botulism outbreaks over 15-year period

Eighty foodborne botulism outbreaks occurred in China involving 55 deaths over a 15-year period, according to a new study.

The top implicated food was home-prepared traditional processed stinky tofu and dried beef. Improper processing or storage were major contributors to outbreaks and initial misdiagnosis occurred in more than a quarter of the 386 cases.

Data from 22 of 31 provinces during 2004 to 2020 showed most outbreaks were reported between June and August, with a sharp peak in January.

The study, published in China CDC Weekly, highlighted key characteristics of foodborne botulism outbreaks that could inform clinicians and public health officials in developing preparedness and response plans. 

Outbreak factors
Xinjiang reported the most followed by Qinghai. The latter accounted for the most illnesses with 101 and 18 deaths.

“This may be related to the fact that local farmers and herders especially in Xinjiang and Qinghai prepared traditional foods — home-made ethnic foods such as stinky tofu, soybean paste stew, and air-dried raw beef from households — using inappropriate or unsafe production processes,” said researchers.

The case-fatality rate decreased from 15 of 26 in 2004 to five of 13 in 2020. The number of outbreaks per year ranged from three to 11.

Households had the largest proportion of outbreaks with 72 of the 80 epidemics. Improper processing and storage were the main contributing factors of foodborne botulinum, accounting for 62 incidents. 

Scientists said targeted continuous education is needed to inform farmers and herdsmen in Xinjiang and Qinghai of the potential risks of botulism from homemade traditional foods.

“It is necessary to standardize the management of processing, storage, and consumption of food raw materials. Preventive messages should focus on not using unsanitary and traditional food processing, changing the bad eating habits of eating raw or half-raw meat, heating and boiling native foods thoroughly to destroy toxins and prevent Clostridium botulinum poisoning.”

Tofu and dried beef were the primary sources of botulism, being linked to 41 out of 80 outbreaks.

Misdiagnosis issues and data gaps
Botulism is a rare but life-threatening condition caused by toxins produced by Clostridium botulinum bacteria. In foodborne botulism, symptoms generally begin 18 to 36 hours after eating a contaminated food. However, they can start as soon as six hours after or up to 10 days later.

Among the 54 identified types of botulinum toxin, BoNT type A was the most frequently identified toxin type, followed by type B.

Misdiagnosis occurred in more than a quarter of cases. This means that patients with botulism were thought to have other illnesses. The case fatality rate in Qinghai was higher than in Xinjiang, which may be due to initial misdiagnosis or delayed diagnosis.

Researchers advised hospitals and local public health officials to stock up on a certain amount of botulinum antitoxin as part of emergency planning.

Data was often incomplete for clinical symptoms, incubation period, and some laboratories couldn’t differentiate between botulinum toxin and serum.

“The epidemiological survey data and the quality of data reporting foodborne Clostridium botulinum surveillance should be improved; a better understanding of the epidemiology of botulism outbreaks can help tailor local prevention and public health response strategies,” said researchers.

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