Virological analyses in collective catering outbreaks in France between 2012 and 2017.

Enteric viruses cause the majority of foodborne illnesses and common symptoms of many foodborne illnesses include vomiting, diarrhea, abdominal pain, and fever. Among the enteric viruses, human Norovirus (NoV) and hepatitis virus (HAV and HEV) are the main viruses suspected to cause foodborne outbreaks and represent a serious public health. The study presents survey tools of viruses in a wide variety of foodstuffs and results obtained during 56 foodborne outbreaks investigation in France between 2012 and 2017. 246 suspected foods were examined for the presence of four human enteric viruses (NoV GI and NoV GII, HAV or HEV) either using methods described in the EN ISO 15216-1 or in house methods. All viral analysis of food samples were performed with the implementation of process control and an external amplification controls. Eighteen of 56 foodborne outbreaks investigated included at least one positive food sample (16/18 NoV, 1/18 HAV and 1/18 HEV). The genomic levels of four viruses detected ranged from < 102 to 107 genome copies per g or per L. This study showed the interest to develop methods for the extraction of viruses in different foodstuffs to increase the possibility to identify the association between viral illness and food consumption.

Development of an extraction method to detect enteric viruses in dressed vegetables.

Food-borne viral infections are caused mainly by noroviruses (NoV) and the hepatitis A virus (HAV), which respectively cause gastroenteritis and hepatitis. Various foods have been implicated in viral outbreaks, including vegetables that are consumed in a variety of forms, often with salad dressing. NF EN ISO procedures (15216-1:2017) propose standard methods for quantifying NoV and HAV in high-risk food categories, such as vegetables, based on viral elution and PEG concentration methods, but these methods are not suitable for composite meals like salads dressed with oily, fatty or emulsified food ingredients. The development of sensitive and reliable techniques for the detection of viruses in these products is therefore needed to ensure the safety of these products. The aim of this study was to develop an RT-qPCR based method for the detection and quantification of NoV and HAV in various vegetables with different dressings. Three methods for recovering NoV and HAV from artificially contaminated dressed vegetables were evaluated. The selected method was based on the use of Trizol reagent and, according to the type of dressing, the limit of detection ranged from 104 to 106 genome copies/g for NoV and from 102 to 103 PFU/g for HAV. The described method can be applied for detecting NoV and HAV in food containing salad dressing for routine diagnosis needs.

Discrimination of infectious and heat-treated norovirus by combining platinum compounds and real-time RT-PCR.

Human noroviruses (NoV) are major agents of foodborne outbreaks. Because of the lack of a standardized cell culture method, real-time reverse transcriptase PCR is now commonly used for the detection of NoV in foodstuffs and environmental samples. However, this approach detects the viral nucleic acids of both infectious and non-infectious viruses and needs to be optimized to predict infectivity for public health risk assessment. The aim of this study was to develop a viability PCR method to discriminate between native and heat-treated virus, for both NoV and its surrogate, murine norovirus (MNV). To this end, screening of viability markers (monoazide dyes, platinum and palladium compounds) was performed on viral RNA, native virus or heat-treated virus, and incubation conditions were optimized with PtCl4, the most efficient viability marker. Multiple MNV molecular models were designed: no impact of amplicon length was observed on inactivated MNV genomic titer; but the 5'NTR, ORF1 and 3'UTR regions resulted in higher reductions than central genomic regions. The optimal viability PCR conditions developed (incubation with 2.5 mM PtCl4 in PBS for 10 min at 5 °C) were finally applied to MNV by performing heat inactivation studies and to native and heat-treated NoV clinical strains. The viability PCR discriminated efficiently between native and heat-inactivated MNV at 72 °C and 80 °C, and efficiently reduced the genomic titer of heat-treated NoV strains. This viability PCR method could be useful to study heat inactivation kinetics of NoV and MNV. It could also be evaluated for the identification of infectious enteric viruses in foodstuffs and environmental samples.