Yunnan sudden death syndrome is a sudden unexplained death from cardiac arrest, which afflicted significant numbers of rural villagers in Yunnan province in southwest China.
Cases almost always occurred during the midsummer rainy season (from June to August), at an altitude of 1,800–2,400 m (5,900–7,900 ft).
[2] The cause of the deaths was unknown until researchers from the Chinese Center for Disease Control and Prevention isolated a significant factor common in every case: a toxic mushroom which was unintentionally gathered and consumed during wild mushroom harvests in the region.
It was determined that families collecting fungi to sell had been eating these mushrooms as they have no commercial value.
[5] In the hours before death, about two-thirds of the victims experienced nausea, dizziness, heart palpitations, seizures and fatigue.