Virus transfer in food production

Multiple outbreaks of human norovirus* (hNoV) have been associated with fresh food, such as soft berries and lettuce. Food handlers are considered to be the source for the introduction of hNoV into food chains, but their contribution to public health risks associated with hNoV remains unknown.

To determine to what extent food handlers contribute to the introduction and spread of hNoV in fresh produce chains, researchers from the Netherlands conducted a study on estimating transfer proportions of hNoV GI.4, GII.4, murine norovirus (MNV-1), and human adenovirus (hAdV-2) between gloved fingertips and raspberries, strawberries, and lettuce, by quantitative RT-PCR and cell culture if applicable. The study showed that virus transfer from gloves to soft berries was generally lower as compared to lettuce for infectious MNV-1 and hAdV-2, respectively. On the other hand the transfer from produce to glove was mostly greater than vice-versa, adding to the likelihood of virus transfer due to cross contamination from contaminated produce via food handlers.

The study also reveals connection between virus transfer proportions and public health risk. Based on a scenario in which a food handler picked raspberries with contaminated fingertips, the result shows that for a pathogen as infectious as hNoV, low transfer proportions may pose a greater public health risk than high transfer proportions, due to a greater viral spread. This discovery shows that prevention of virus contamination on food handlers’ hands is crucial for food safety.

*The viruses are transmitted by faecally contaminated food or water; by person-to-person contact; and via aerosolization of the virus and subsequent contamination of surfaces. Noroviruses are the most common cause of viral gastroenteritis in humans, and affect people of all ages.