Ghent University, Faculty of Bioscience Engineering, Department of Food Safety and Food Quality, Laboratory of Food Microbiology and Food Preservation, Coupure Links 653, 9000 Ghent, Belgium.
Int J Food Microbiol. 2011 Dec 15;151(3):261-9. doi: 10.1016/j.ijfoodmicro.2011.09.013. Epub 2011 Sep 17.
Foodborne viruses, especially noroviruses (NoV), are increasingly reported as the cause of foodborne outbreaks. NoV outbreaks have been reported linked to fresh soft red fruits and leafy greens. Belgium, Canada and France were the first countries to provide data about the prevalence of NoV on fresh produce. In total, 867 samples of leafy greens, 180 samples of fresh soft red fruits and 57 samples of other types of fresh produce (tomatoes, cucumber and fruit salads) were analyzed. Firstly, the NoV detection methodology, including virus and RNA extraction, real-time RT-PCR and quality controls were compared among the three countries. In addition, confirmation and genotyping of the NoV strains was attempted for a subset of NoV positive samples using conventional RT-PCR targeting an alternative region followed by sequencing. Analysis of the process control showed that 653, 179 and 18 samples of the leafy greens, soft red fruits and other fresh produce types were valid for analysis based on the recovery of the process control. NoV was detected by real-time RT-PCR in 28.2% (N=641), 33.3% (N=6) and 50% (N=6) of leafy greens tested in Canada, Belgium and France, respectively. Soft red fruits were found positive by real-time RT-PCR in 34.5% (N=29) and 6.7% (N=150) of the samples tested in Belgium and France, respectively. 55.5% (N=18) of the other fresh produce types, analyzed in Belgium, were found NoV positive by real-time RT-PCR. Conventional RT-PCR resulted in an amplicon of the expected size in 19.5% (52/266) of the NoV positive samples where this assay was attempted. Subsequent sequencing was only successful in 34.6% (18/52) of the suspected amplicons obtained by conventional RT-PCR. From this study, using the described methodology, NoV genomes were frequently detected in fresh produce however sequence confirmation was not successful for the majority of the samples tested. Infection or outbreaks were rarely or not known to be related to the NoV positive samples. With the increase in sensitivity of the detection methodology, there is an increasing concern about the interpretation of positive NoV results by real-time amplification. Strategies to confirm the results by real-time RT-PCR should be developed in analogy with the detection of microbial pathogens in foods. Detection might indicate contact with NoV in the fresh produce chain. Consequently, a potential risk for infection cannot be excluded but the actual risk from RT-PCR NoV positive produce is still unknown. Studies should be designed determining the probability of infection related to the presence or levels of NoV genomic copies.
食源性病毒，尤其是诺如病毒（NoV），越来越多地被报道为食源性疾病暴发的原因。NoV 暴发已被报道与新鲜软红水果和叶菜有关。比利时、加拿大和法国是第一批提供有关新鲜农产品中 NoV 流行情况数据的国家。总共分析了 867 份叶菜、180 份新鲜软红水果和 57 份其他类型的新鲜农产品（西红柿、黄瓜和水果沙拉）。首先，比较了三个国家之间的 NoV 检测方法，包括病毒和 RNA 提取、实时 RT-PCR 和质量控制。此外，还尝试使用针对替代区域的常规 RT-PCR 对部分 NoV 阳性样本进行 NoV 株的确认和基因分型，然后进行测序。过程控制分析表明，基于过程控制的恢复，叶菜、软红水果和其他新鲜农产品类型的 653、179 和 18 个样本可用于分析。在加拿大、比利时和法国进行的测试中，实时 RT-PCR 分别检测到 28.2%（N=641）、33.3%（N=6）和 50%（N=6）的叶菜中存在 NoV。在比利时和法国进行的测试中，实时 RT-PCR 分别发现软红水果的阳性率为 34.5%（N=29）和 6.7%（N=150）。在比利时进行的分析中，其他新鲜农产品类型的 55.5%（N=18）通过实时 RT-PCR 检测为 NoV 阳性。在尝试该检测的 52/266 份 NoV 阳性样本中，常规 RT-PCR 产生了预期大小的扩增子。随后的测序仅在常规 RT-PCR 获得的疑似扩增子的 34.6%（18/52）中成功。从这项研究中可以看出，使用描述的方法，在新鲜农产品中经常检测到 NoV 基因组，但对大多数测试样本的序列确认并不成功。感染或暴发很少或不知道与 NoV 阳性样本有关。随着检测方法灵敏度的提高，人们越来越担心实时扩增对 NoV 阳性结果的解释。应该制定通过实时 RT-PCR 确认结果的策略，与食品中微生物病原体的检测类似。检测可能表明在新鲜农产品链中接触到了 NoV。因此，不能排除感染的潜在风险，但实时 RT-PCR NoV 阳性产品的实际风险仍未知。应设计研究确定与 NoV 基因组拷贝的存在或水平相关的感染可能性。
