Consumption of viscera as the most important risk factor in the largest outbreak of shellfish poisoning in Hong Kong, 2005.

Poisoning from shellfish toxins is associated with significant morbidity worldwide. During 10-15 March 2005, 36 clusters of shellfish poisoning related to consumption of fresh scallops (Atrina vexillum) were reported to the Center for Health Protection, Department of Health Hong Kong. We conducted a case-control study to identify the risk factors associated with shellfish poisoning. Detailed demographic, clinical, shellfish consumption data of these subjects were collected using standardized questionnaires. Fifty-eight cases and 44 controls were identified. The mean age for the cases was 37.5 years (range 10-81 years); 45% (n=26) were male. Ninety-five percent had onset of symptoms within 12 hours of consumption of scallops (range: 10 minutes to 30 hours, median: 45 minutes). Dizziness (87.9%) and blurred vision (53.4%) were the predominant symptoms. The mean number of pieces of scallop meat and viscera taken by the cases were 3.7 and 3.6, respectively, significantly higher than that for the controls, which were 1.6 (p<0.001) and 0.5 (p<0.001), respectively. Forty-two percent (n=22) and 19% (n=7) of cases and controls, respectively, took soup/sauce from the same dish that was cooked with the scallops (p=0.02). Consumption of scallop viscera was identified as the only significant risk factor (Adjusted OR=9.93, p=0.001) after adjusting for other risk factors. The result show that consumption of scallop viscera is an important risk factor for shellfish poisoning. The public should be warned specifically in health education messages to avoid eating viscera of scallops.