Nine people died in China after eating food contaminated with 20 to 30 times the lethal dose of a toxin, according to a study.

In October 2020, nine people in Jidong County, Heilongjiang Province died after consuming a homemade fermented corn flour product called sour soup for breakfast. The food was contaminated by Burkholderia cocovenenans, which can produce bongkrekic acid. In China, B. cocovenenans is often called Pseudomonas cocovenenans.

Bongkrekic acid was detected in food and biological samples at 330 milligrams per kilogram (mg/kg) and 3 milligrams per liter (mg/L), respectively. The amount of bongkrekic acid consumed by the cases was 22 to 33 times the lethal dose for humans, according to the study published in China CDC Weekly.

Consumption of fermented corn flour products, deteriorated fresh tremella — an edible fungus — or black fungus and metamorphic starch products may cause bongkrekic acid poisoning. Health education should be strengthened so that homemade-starch-fermented food is avoided. The researchers also said items that have been kept for a long time should not be consumed.

Incident timeline
Surveillance data shows 15 bongkrekic acid poisoning “incidents”, 136 patients and 36 deaths were reported from 2010 to 2019 in mainland China. Sour soup poisoning caused one of these incidents with four deaths.

In October, Jidong County CDC received a report of a suspected food poisoning incident affecting a family in Sihai Community, Xingnong Town. Twelve people from five families had gathered for lunch and dinner, and the day after they had breakfast together. Nine consumed the sour soup while all 12 had the other foods.

The nine people who ate the soup then developed gastrointestinal symptoms such as nausea, vomiting, and abdominal pain and all of them died after treatment. One patient returned home after receiving prescription medication from an outpatient department but later died.

Because those who made the food died, it is impossible to know all the details of how it was prepared but it is thought making of the contaminated homemade sour soup started one year before the incident when the corn was soaked in water for about a month to ferment. After mill grinding, corn husks were filtered out in the water, and delicate parts were kept to be dried in flour bags and formed into dough and then noodles. It was consumed as soon as the noodle-based sour soup was ready and the rest of the dough was put in the refrigerator and frozen.

In fall, because the refrigerator was used for other foods, the dough was made into cornmeal powder and then stored in the fridge again to save space. After the corn dough was taken out, it was exposed to air outside and covered with a porous plastic net. After drying for a day, it was moved to dry in the house because of cloudy and rainy weather.

Likely contamination point
The investigation revealed that the nine patients included four males and five females with an age range of 45 to 72 years old. It confirmed the poisoning was caused by bongkrekic acid when bacteria contaminated the corn flour and was used to make the sour soup.

It is not clear how the corn flour used was contaminated but the implicated sour soup was made with the same batch that was used the year before when no problems were reported.

The corn dough was likely contaminated when it was dried outside, according to the research. The natural air drying speed was slow as the environment likely had poor ventilation, high relative humidity, and a suitable temperature for bacterial growth. These factors provide favorable conditions for the bacteria to multiply and produce the toxin. Bongkrekic acid is heat-stable so is not destroyed during cooking.

It took five and six days to get the qualitative and quantitative test results in this incident. If people were treated in time at a hospital capable of dealing with severe poisoning, some may not have died, said researchers.