The final straw: berries and viruses.

Malak Esseili, University of Georgia

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Food & Environmental Virology-I (Food)

Human norovirus (HuNoV) and hepatitis A virus (HAV) are responsible for several foodborne outbreaks associated with fresh or frozen berries. During epidemiological investigations, berries are tested for viruses using either the BAM 26 or the ISO 15216 standardized methods. However, both methods rely on the detection of viral RNA by RT-qPCR, which does not necessarily indicate the presence of infectious viruses. The overall goal of this research was to determine the survival of infectious viruses on whole berries and in berry smoothies under refrigeration and as the berries undergo digestion, the limit of detections for the standardized methods, and the relationship between RT-qPCR Ct values and infectivity titers of viruses. Viruses were spiked on strawberries, and then recovered using either the BAM or ISO methods, followed by quantification using RT-qPCR and TCID50 or human intestinal enteroid (HIE) infectivity assays. Our results showed that infectious viruses were stable in berry smoothies stored under refrigeration for 2h, as well as during the oral, gastric, and intestinal digestion phases. Infectious viruses also persisted on whole berries stored under refrigeration for at least 7 days. The RT-qPCR Ct limit of detection for infectious viruses using BAM and ISO methods were not significantly different from each other’s. Multiple logistic regression model indicated that there is a low probability of directly recovering infectious viruses from strawberries when Ct values are greater than 36. Overall, this study provides better insights on infectious virus persistence in berries and on the interpretation of virus Ct values obtained from berries.