Detection and Typing of Norovirus from Frozen Strawberries Involved in a Large-Scale Gastroenteritis Outbreak in Germany

Abstract

During September/October 2012, a norovirus gastroenteritis outbreak affecting about 11,000 people occurred in Germany. Epidemiological studies suggested that frozen strawberries represented the vehicle of infection. We describe here the analysis of frozen strawberries for the presence of norovirus. Samples were taken by applying a stratified subsampling scheme. Two different methods for virus extraction from strawberries were compared. First, viruses were eluted from strawberries under alkaline conditions and concentrated using a polyethylene glycol precipitation. Second, ultrafiltration was applied for concentration of viruses rinsed off of the berries. In both cases, RNA was extracted and analyzed by real-time RT-PCR. Application of the ultrafiltration method generally resulted in a lower detection rate. Noroviruses were detected in 7/11 samples derived from the lot of strawberries implicated in the outbreak using the precipitation method. Typing of norovirus revealed three different genotypes including a combination of norovirus genotype II.16 (viral polymerase) and II.13 (viral capsid). This genotype combination was also found in some of the patients that were involved in the outbreak, but that had not been reported in Germany so far. In conclusion, heterogeneously distributed noroviruses in frozen strawberries can be detected by applying an optimized combination of sampling procedures, virus extraction methods, and real-time RT-PCR protocols. The detection of several different genotypes in the strawberries may suggest contamination from sewage rather than from a single infected food handler.

Genetic and Epidemiologic Trends of Norovirus Outbreaks in the United States from 2013 to 2016 Demonstrated Emergence of Novel GII.4 Recombinant Viruses

“…This novel GII.P16-GII.2 recombinant virus caused at least seven outbreaks in the United States in 2016 as early as August. While GII.P16 polymerases associated with different GII capsids have circulated for decades (17,18,42,(49)(50)(51)(52)(53)(54) and caused occasional outbreaks (16,55,56), the GII.P16 polymerase associated with GII.4 Sydney and GII.2 genotypes appears to have made these viruses evolve toward greater transmissibility.…”

Evidence of the Internalization of Animal Caliciviruses via the Roots of Growing Strawberry Plants and Dissemination to the Fruit

“…Infected food handler contamination and exposure to fecally contaminated water are thought to be the most frequent modes of human NoV contamination of foods (2,5,10,18). The use of irrigation water that is contaminated with fecal matter is considered a significant cause of viral contamination in soft berries (19)(20)(21)(22). A multicountry study conducted in Europe investigating human NoV prevalence in soft red fruit obtained directly from processing companies or retail markets found viral RNA in 7 to 34% of samples (2,22).…”

“…However, in approximately 50% of the single-commodity human NoV outbreaks, the point of contamination could not be determined, and viral contamination prior to preparation could have occurred in these instances (2). In September and October 2012, a large outbreak of human NoV associated with the consumption of frozen strawberries sickened nearly 11,000 individuals in Germany (19). Genotyping revealed GI.9, GII.6, and GII.13/GII.16 norovirus strains in the implicated berries and in patient stool samples (19).…”

Potentiometric Investigation of the Dynamics of Bacteriophage - Induced Potassium Ion Efflux in Escherichia coli

“…Bacterial debris was removed by centrifugation and the supernatant was sterilized using 0.22 µm syringe filters. Filter sterilized phage lysate was precipitated with 10% polyethylene glycol (PEG 8000) at 4°C overnight based on the procedure described for purification of Norovirus [16]. After precipitation, the lysate was centrifuged at 8000 rpm for 15 minutes and the pellets were resuspended in the phage buffer (10 mM Na 3 PO 4 , 137 mM NaCl, and 0.2% MgSO 4 ; pH 7.2).…”