An Epidemiologic Investigation of Haff Disease Outbreak in China, 2016

Water or foodborne

Background:
Haff disease is unexplained rhabdomyolysis that occurs after eating cooked seafood. The etiology has not yet been determined. In July, 2016, the National Foodborne Disease Surveillance System (NFDSS) detected a >20-fold increase in Haff disease. We investigated to describe the epidemiology and clinical characteristics, trace back of implicated seafood vectors.

Methods:
A case was defined as illness in a person with unexplained rhabdomyolysis after eating seafood in the 24 hours before onset of symptom from June to August 2016. We interviewed all patients and reviewed their medical records for demographic and clinical information, food exposures and personal risk factors. We interviewed patients, crayfish sellers and fishermen to trace the implicated crayfish lots.

Results:
Total 1,347 cases were reported in 9 provinces from June 27 to August 24, 2016. 72.9% (982) of cases occurred in 3 nearby cities, which are located in the middle and lower reach of the Yangtze River. The Epi-curve reached its peak from July 16-31 after heavy rainfall. 86.3% (847) of 982 cases were interviewed completely. The most common clinical features were myalgia (100%), myasthenia (52%) and markedly elevated (5-fold levels) of creative kinase (79%). All 982 cases ingested cooked crayfish. The median incubation period was 6 hours (range: 0.5-23 hours). 70% of implicated crayfish were caught on the shores of the Yangtze River. The quantity of catching crayfish was 5-folded increased compare with the previous years.

Conclusion:
The largest Haff disease outbreak was caused by consumption of cooked crayfish, caught on the shores of the Yangtze River. A public health announcement was made based on our finding. We recommend enhancing NFDSS and continue the ongoing investigation to elucidate the cause of Haff disease.

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