Efficacy of washing produce in removing human coronavirus OC43 and murine norovirus

Abstract

Aims: Fresh produce is often a vehicle for the transmission of foodborne pathogens such as human norovirus. Thus, it is recommended to wash the surface of produce before consumption, and one of the most common ways to wash produce is by rinsing under running tap water. This study determined the effectiveness of removal of human coronavirus-OC43 (HCoV-OC43), as a surrogate for severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and murine norovirus-1 (MNV-1), as a surrogate for human norovirus, from contaminated lettuce, apples and cucumbers.

Methods and results: The produce surfaces were artificially inoculated in conjunction with faecal material to represent natural contamination. Rinsing under tap water for 10 s at 40 ml/s removed 1.94 ± 0.44, 1.42 ± 0.00 and 1.42 ± 0.42 log of HCoV-OC43 from apple, cucumber and lettuce respectively. The same washing technique removed 1.77 ± 0.17, 1.42 ± 0.07 and 1.79 ± 0.14 log of MNV-1 from apple, cucumber and lettuce respectively. This washing technique was effective at reducing a significant amount of viral contamination, however, it was not enough to eliminate the entire contamination. There was no significant difference in the reduction of viral load between the two viruses, nor between the three surfaces tested in this study.

Conclusions: Our data suggest that washing under tap water would be an efficient way of reducing the risk of foodborne viral transmission only if the level of contamination is less than 2 log PFU.

Significance and impact of study: This study demonstrates that running tap water was effective at reducing the amount of infectious HCoV-OC43 and MNV on produce surfaces, and washing produce continues to be an important task to perform prior to consumption to avoid infection by foodborne viruses, particularly for foods which are eaten raw.

Keywords: human coronavirus OC43; murine norovirus-1; produce; tap water; wash.

FIGURE 1

Schematic representation of the experimental procedures in this study.

FIGURE 2

Concentration of infectious HCoV‐OC43 before and after rinsing with tap water for 10 s at a rate of 40 ml/s for the three produce surfaces tested. TCID₅₀/ml values were converted to PFU/ml by multiplying by 0.7 (Wang. 2013). The data are from three independent experiments. *p < 0.05, calculated by t‐test.

FIGURE 3

Concentration of infectious MNV‐1 before and after rinsing with tap water for 10 s at a rate of 40 ml/s for the three produce surfaces tested. The data are from three independent experiments. *p < 0.05, calculated by t‐test.