Free chlorine concentration x time values for inactivation of human Norovirus in leafy greens

Human noroviruses (hNoVs) are a known public health concern associated with the consumption of leafy green vegetables. While a number of studies have investigated pathogen reduction on the surfaces of leafy greens during the postharvest washing process, there remains a paucity of data on the level of treatment needed to inactivate viruses in the wash water, which is critical for preventing cross-contamination. The objective of this study was to quantify the susceptibility of hNoV GI, hNoV GII, murine norovirus (MNV), and bacteriophage MS2 to free chlorine in whole leaf, chopped romaine, and shredded iceberg lettuce industrial leafy green wash waters, each sampled three times over a 4-month period. A suite of kinetic inactivation models was fit to the viral reduction data to aid in quantification of concentration ? time (CT) values. Results indicate that 3 log10 infectivity reduction was achieved at CT values of less than 0.2 mg-min/L for MNV and 2.5 mg-min/L for MS2 in all wash water types. CT values for 2 log10 molecular reduction of hNoV GI in whole leaf and chopped romaine wash waters were 1.5 and 0.9 mg-min/L, respectively. For hNoV GII, CT values were 13.0 and 7.5 mg-min/L, respectively. In shredded iceberg wash water, 3 log10 molecular reduction was not observed for any virus over the time course of experiments. These findings demonstrate that noroviruses may exhibit genogroup dependent resistance to free chlorine and emphasize the importance of distinguishing between genogroups in hNoV persistence studies. Importance Postharvest washing of millions of pounds of leafy greens is performed daily in industrial processing facilities with the intention of removing dirt, debris, and pathogenic microorganisms prior to packaging. Modest inactivation of pathogenic microorganisms (less than 1-2 log10) is known to occur on the surfaces of leafy greens during washing. Therefore, the primary purpose of the sanitizing agent is to maintain microbial quality of postharvest processing water in order to limit cross-contamination. This study modeled viral inactivation data and quantified the free chlorine CT values that processing facilities must meet in order to achieve the desired level of hNoV GI and GII reduction. Disinfection experiments were conducted in industrial leafy green wash water collected from a full-scale fresh produce processing facility in the U.S., and hNoV GI and GII results were compared with surrogate molecular and infectivity data. Access to document 'Stability of and Attachment to Lettuce by a Culturable Porcine Sapovirus Surrogate for Human Caliciviruses' ? Nathan Dunkina (a), Shih-Chi Weng (b), Joseph G. Jacangelo (a,b,c) &?Kellogg J. Schwaba (b) (a) Department of Environmental Health and Engineering, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, USA(b) JHU/MWH-Stantec Alliance, Johns Hopkins University, Baltimore, Maryland, USA(c) MWH-Stantec, Pasadena, California, USA