Inactivation of Norovirus during Smoked Salmon Storage

Introduction: Human norovirus mainly caused gastroenteritis through intake of raw seafood and vegetables with a low infectious dose of 10 to 100 viral particles. Since the consumption of smoked salmon has been recently increased, the possibility for norovirus outbreak by smoked salmon has also increased.

Purpose: The objective of this study was to determine the survival of norovirus in smoked salmon using murine norovirus as a norovirus surrogate at low temperature.

Methods: Murine norovirus was inoculated into 25 g of smoked salmon samples at four log PFU/g, and the smoked salmon samples were stored aerobically at 4°C (three days) and 20°C (two days). Enumeration of murine norovirus on smoked salmon was conducted by plaque assay with RAW 264.7 cells. For the initial titer plaque assay, RAW 264.7 cells were seeded into six-well plates at a concentration of 5×10⁵ viable cells in two ml of minimum essential media to each well. The Baranyi model was fitted to the quantitative data for murine norovirus to calculate death rate (log PFU/g/h).

Results: The results of initial titer plaque assay showed that inoculate virus counts were 4.09 log PFU/g. Murine norovirus in smoked salmon was rapidly inactivated less than 48 h at 20°C. Murine norovirus titer were decreased from 4.09 to 1.5 log PFU/g at 4°C for 72 h. Death rates ranged from -0.02 (4°C) to -0.06 log PFU/g/h (20°C).

Significance: The results indicate that norovirus can survive at cold temperature rather than high temperature. Therefore, low amounts of norovirus remained at cold temperature storage can be infected from smoked salmon to human.