Evaluation of the persistence of infectious human noroviruses on food surfaces by using real-time nucleic acid sequence-based amplification

Noroviruses (NoV) are the major cause of nonbacterial gastroenteritis. However, there is no published study to ascertain their survival on foodstuffs which are directly related to human health risk. In the present study, we developed a rapid, simple, and sensitive real-time nucleic acid sequence-based amplification (NASBA) combined with an enzymatic treatment for distinguishing infectious from noninfectious human NoV. The developed method was validated using spiked ready-to-eat food samples. When feline calicivirus (FCV) was used as a NoV surrogate in the preliminary assays, it appeared more sensitive to heat inactivation and enzymatic pretreatment than the human NoV. This suggests that FCV may not be an ideal model for studying NoV. Our results reveal clearly that the developed enzymatic pretreatment/real-time NASBA combination successfully distinguished the infectious from heat-inactivated NoV. Moreover, we demonstrate that NoV survived for at least 10 days on refrigerated ready-to-eat foods, such as lettuce and turkey. However, the survival rate was higher on turkey than on lettuce, probably because of their different surface natures. The approach developed in this study may be suitable for more in-depth studies of the persistence and inactivation of human NoV and may be applied to other nonculturable RNA viruses. Moreover, the evaluation of infectious NoV survival provided valuable information concerning its persistence on ready-to-eat food.