The family was poisoned by toxic bongkrekic acid found in noodles, local authorities told the state-run Global Times, while ruling out the possibility of intentional poisoning.
Following the death, the National Health Commission on Tuesday issued an urgent warning for people to avoid making and eating foods with fermented rice and flour, reported the China Daily.
The family of 12, living in the Jixi city of Northeast China's Heilongjiang province, had gathered on 5 October for breakfast. While nine of the family ate the homemade noodles, also known as Suantangzi, the younger members did not eat it because they did not like the taste. Suantangzi is a thick type of noodle made from fermented corn flour.
The nine who ate the noodles felt ill within hours of eating and eight were confirmed dead by 11 October. A ninth member of the family, a 47-year-old woman surnamed Li, received treated in hospital but finally died on Monday.
A high concentration of bongkrekic acid, a respiratory toxin produced by the bacterium pseudomonas cocovenenans, was detected in the corn noodles and in the gastric fluid of the deceased, the provincial health commission was quoted by China Daily as saying.
Gao Fei, director of food safety at the Heilongjiang Centre for Disease Control and Prevention, told China News Service that the results of bongkrekic acid poisoning can often be fatal.
“It can cause serious damage to many human organs including the liver, kidneys, heart, and brain,” Mr Gao said.
According to experts, currently there is no specific antidote and if poisoned, the fatality rate can be between 40 per cent and 100 per cent.
The symptoms of bongkrekic poisoning begin within a few hours of eating the contaminated food and include stomach pain, sweating, general weakness and eventual coma. Death can then occur within 24 hours.