Differences in the effectiveness of the high-efficient concentrated pretreatment method on the norovirus detection in oysters and mussels

Oysters and mussels are important vectors for norovirus (NoV). An efficient pretreatment method for NoV detection in oysters based on ISO 15216-2:2019 was established in our previous work, but its effectiveness for other types of shellfish remains unknown. Therefore, this study systematically compared the differences between the standard and modified ISO methods in detecting NoV for oysters and mussels. Using the standard ISO method, the recovery rates of NoV in oysters (2.10 +/- 0.80 %) and mussels (2.39 +/- 0.56 %) were comparable (p > 0.05, unpaired t-test). In contrast, the virus recovery rates in oysters (19.83 +/- 3.64 %) and mussels (46.96 +/- 3.55 %) were both significantly improved by the modified method. Also, a significant difference was found between the virus recovery rates in two shellfish (p < 0.05, unpaired t-test), resulting in a 2.09-fold difference in their virus concentrations. Additionally, the limits of detection at 95 % probability of the modified ISO method for oysters and mussels could both reach 3.33 x 103 copies/g of digestive glands. Finally, the modified ISO method has been successfully applied in commercial oysters (14/27, 51.85 %) and mussels (15/23, 65.22 %), and the results indicated a significant difference in NoV recovery rates between two shellfish (p < 0.05, one-way analysis of variance). In summary, the modified ISO method showed higher virus recovery rates than the standard ISO method, which would be used as an essential tool for NoV detection in oysters and mussels.