Outbreak of Haff Disease along the Yangtze River, Anhui Province, China, 2016.

We investigated a large outbreak of Haff disease that occurred along the Yangtze River in Anhui Province, China, in 2016. Of the 672 cases identified during the outbreak, 83.3% (560/672) occurred in Wuhu and Ma'anshan. Patients experienced myalgia (100%) and muscle weakness (54.7%). The mean value of myoglobin was 330 + 121.2 ng/mL and of serum creatine kinase 5,439.2 + 4,765.1 U/L. Eating crayfish was the only common exposure among all cases; 96.8% (240/248) of implicated crayfish were caught on the shores of the Yangtze River or its connected ditches. Mean incubation period was 6.2 + 3.8 hours. This case-control study demonstrated that eating the liver of crayfish and eating a large quantity of crayfish were associated with an increased risk for Haff disease. The seasonal increases in crayfish population along the Yangtze River might explain the seasonal outbreaks of Haff disease.