Norovirus contamination of oysters is the lead cause of non-bacterial gastroenteritis and a significant food safety concern for the oyster industry. Here, norovirus reduction from Pacific oysters (Crassostrea gigas), contaminated in the marine environment, was studied in laboratory depuration trials and in two commercial settings. Norovirus concentrations were measured in oyster digestive tissue before, during and post-depuration using the ISO 15216-1 quantitative real-time RT-PCR method. Results of the laboratory-based studies demonstrate that statistically significant reductions of up to 74% of the initial norovirus GII concentration was achieved after 3 days at 17–21 °C and after 4 days at 11–15 °C, compared to 44% reduction at 7–9 °C. In many trials norovirus GII concentrations were reduced to levels below 100 genome copies per gram (gcg⁻¹; limit of quantitation; LOQ). Virus reduction was also assessed in commercial depuration systems, routinely used by two Irish oyster producers. Up to 68% reduction was recorded for norovirus GI and up to 90% for norovirus GII reducing the geometric mean virus concentration close to or below the LOQ. In both commercial settings there was a significant difference between the levels of reduction of norovirus GI compared to GII (p < 0.05). Additionally, the ability to reduce the norovirus concentration in oysters to < LOQ differed when contaminated with concentrations below and above 1000 gcg⁻¹. These results indicate that depuration, carried out at elevated (> 11 °C) water temperatures for at least 3 days, can reduce the concentration of norovirus in oysters and therefore consumer exposure providing a practical risk management tool for the shellfish industry.

牡蛎的诺如病毒污染是非细菌性胃肠炎的主要原因，也是牡蛎产业的重大食品安全问题。在这里，来自太平洋牡蛎（Crassostrea gigas）的诺如病毒减少，在实验室净化试验和两个商业环境中对海洋环境中的污染进行了研究。使用 ISO 15216-1 定量实时 RT-PCR 方法在净化前、净化期间和净化后测量牡蛎消化组织中的诺如病毒浓度。基于实验室的研究结果表明，在 17–21 °C 下 3 天后和在 11–15 °C 下 4 天后，初始诺如病毒 GII 浓度降低了多达 74% 的统计显着降低，相比之下降低了 44%在 7–9 °C。在许多试验中，诺如病毒 GII 的浓度降低到每克 100 个基因组拷贝以下的水平 (gcg ^-1; 定量限；定量）。两个爱尔兰牡蛎生产商经常使用的商业净化系统也评估了病毒减少情况。诺如病毒 GI 减少了 68%，诺如病毒 GII 减少了 90%，使几何平均病毒浓度接近或低于 LOQ。在两种商业环境中，诺如病毒 GI 的降低水平与 GII 相比存在显着差异（p  < 0.05）。此外，当牡蛎中的诺如病毒浓度低于和高于 1000 gcg ^-1时，将其降低至 < LOQ 的能力不同. 这些结果表明，在升高的 (> 11 °C) 水温下进行至少 3 天的净化，可以降低牡蛎中诺如病毒的浓度，从而为贝类行业提供实用的风险管理工具。