Effect of Wash Treatments on Reducing Human Norovirus on Iceberg Lettuce and Perilla Leaf

Human noroviruses (NoVs) are major causes of nonbacterial gastroenteritis; they are transmitted by food and water, as well as person-to-person. The consumption of contaminated raw or uncooked food such as vegetables and fruits has been identified as a common source of human NoV outbreaks. In an effort to understand the survival and persistence of human NoVs on fresh produce, the efficacy of washing treatments in the removal of human NoVs from vegetables was evaluated. This study used artificially contaminated vegetables (iceberg lettuce and perilla leaf), and washing was done with tap water for convenience. Wash treatments included immersion in water, rinsing with running water, and a combination of immersion and rinsing (treatments I to III, respectively). The effect of a class I detergent, a commercial product used for washing fruits and vegetables, was also evaluated (treatment IV). After the wash treatments, the remnants of human NoVs on samples were measured via real-time reverse transcriptase PCR. The results varied among treatments and by vegetable. For iceberg lettuce, a reduction of 0.9 log was noted in the treatment Ill group. The wash treatment was more effective in the perilla leaf samples: each treatment significantly reduced the numbers of human NoVs (0.69- to 1.29-log reduction). These data demonstrated that wash treatments reduced numbers of virus from the surfaces of the vegetables. Therefore, washing would seem to be a basic step in reducing numbers of virus in food preparation and in viral transmission routes.