The need for harmonization in detection of human noroviruses in food

Noroviruses (NoV) have been recognized worldwide as a leading cause of foodborne gastroenteritis over the last decade. A broad range of foods- shellfish, fresh produce, and ready-to-eat/catered foods-has been implicated in NoV foodborne outbreaks. The recognition of NoV as an important food pathogen has been aided by the development of sensitive molecular methods for detection of the NoV genome. However, despite advances, NoV detection is still hampered by several limitations. First, NoV detection can often only be implemented by expert laboratories due to the complexity of the virus extraction step, which in most protocols is cumbersome and labor-intensive. Moreover, a very wide selection of automated methods for virus extraction from foods is available, so selection of an adequate method is not straightforward. On the other hand, automated systems have been made available or the RNA purification and real-time RT-PCR (RT-qPCR) is considered the gold standard for detection of NoV. Second, correct interpretation of real-time PCR results is often difficult. From a technical point of view, the interpretation of the often nonsigmoidal amplification curves remains difficult, even for experts. From a food safety perspective, interpretation of very high Cq (or Ct) values-and thus, of low viral genomic copy numbers-is not straightforward, as RT-(q)PCR merely detects the presence of viral genomic material that is not necessarily linked to the presence of infectious viral particles. Despite efforts, both limitations have not completely resolved thus far. Harmonization may be a first step to comprehend and deal with these limitations. The current review provides an overview of a number of validated methods that have been published by food safety and other authorities.