The likelihood of cross‐contamination of head lettuce by E. coli O157:H7, Salmonella and norovirus during hand harvest and recommendations for glove sanitizing and use.

Mandatory glove use when handling raw produce and the practice of sanitizing gloves with bleach is common despite uncertainty that these practices improve the safety of foods. Here, the impacts of glove use (frequency of changing and glove composition) and sanitation (using bleach and a novel sanitizer developed at UGA) on cross-contamination of raw head lettuce by bacterial (E. coli O157:H7, Salmonella) and viral (norovirus) pathogens during harvest will be investigated. Since build-up (soil and lettuce residue) on gloves likely impacts transfer of pathogens to and from gloves, accumulation of these materials on gloves over time (0.5, 1,2 and 4 hr) will be quantified for volunteer harvesters wearing either rubber or nitrile gloves. In the lab, natural accumulation will be mimicked on gloves and the likelihood of pathogen transfer to gloves and head lettuce will be investigated. Finally, a novel sanitizer will be evaluated for its efficacy in removing organic material accumulation and inactivating pathogens on gloves as compared to bleach. This study will provide a scientific basis for making recommendations on glove use and sanitation during harvesting head lettuce and will contribute to improving the safety of fresh produce.

In response to growing concerns regarding the safety of raw produce, the mandatory use of gloves when handling raw produce and the practice of sanitizing gloves with bleach (in rinse buckets) has become common in the leafy green industry. However, it is uncertain that these practices actually improve the safety of leafy greens. In this study, the impacts of glove use (frequency of changing and glove composition) and sanitation (using bleach and a novel sanitizer developed at UGA) on cross‐contamination of raw head lettuce by bacterial (E. coli O157:H7, Salmonella) and viral (norovirus) pathogens during harvest will be investigated. Since build‐up (soil and lettuce material) on gloves likely impacts transfer of pathogens to and from gloves, accumulation of this material on gloves over time (0.5, 1, 2, and 4 hr) will be quantified for volunteer harvesters wearing either rubber or nitrile gloves. To do this, we will first optimize methods for characterizing and quantifying levels of soil and lettuce latex residues accumulating on gloves by carbon and nitrogen isotopic ratio analyses. Next, natural accumulation of organic material on gloves will be quantified by conducting a field study in which the gloves of harvesters/corers will be collected and analyzed using the optimized methods. Once natural accumulation of organic material on gloves is characterized and soil to latex ratios are quantified for each harvest time increment and for each glove type, a subset of these levels (high, medium, low and none) will be mimicked on gloves in the lab using a mock organic material carefully formulated with varying ratios of soil and lettuce latex. Next, the likelihood and degree of pathogen transfer to gloves from mock contaminated soil and lettuce, and to lettuce from mock contaminated gloves will be investigated. Mock contaminated [bacterial (E. coli O157:H7, Salmonella) or viral (murine norovirus, a surrogate for human norovirus) pathogens] soil or lettuce will be touched by a pathogen‐free, gloved hand to determine cross‐contamination of gloves by soil or lettuce. Similarly, for investigating how many lettuce heads can become contaminated following a single glove contamination event, pathogens will be inoculated on gloves and multiple lettuce heads will be touched. Pathogens eluted from the gloves or lettuce will be quantified by standard culture or plaque assays. Finally, a novel sanitizer will be evaluated for its efficacy in removing organic material and inactivating pathogens on gloves as compared to bleach. To do this, gloves mock coated in 4 concentrations of organic material (high, medium, low and none) and inoculated with bacterial or viral pathogens will be exposed to varying concentrations of a novel levulinic acid plus SDS sanitizer or bleach, with or without 1 M NaCl (which enhances dissociation of viruses from hard surfaces). After neutralization, reductions in viable bacteria or virus will be assayed from gloves. The results of this study will provide a scientific basis for making recommendations on glove use (frequency of changing and type) and sanitation during harvesting head lettuce and will contribute to improving the safety of fresh produce.

Objective 1. Develop and evaluate tools for characterizing and quantifying the accumulation of organic material (soil and lettuce latex) on the gloves during the process of harvesting head lettuce. 

Objective 2. Conduct a field study in the Salinas Valley area whereby gloves (rubber and nitrile) used by harvesters/corers in the field at specific time intervals (0.5, 1, 2, and 4 hrs) during a typical day will be collected for subsequent measurement of organic material accumulation. 

Objective 3. Using both field and laboratory analyses, determine the amount of organic material (ratio of soil and lettuce latex) that accumulated on gloves collecting in the field. 

Objective 4. Create a mock soil/latex solution in the lab that, once applied to gloves, will mirror three levels (high, medium and low) of organic material (have the same ratios of soil and latex) on gloves collected during the field study. 

Objective 5. Determine the likelihood and degree of pathogen (E. coli O157:H7, Salmonella and norovirus) transfer to "used" gloves (rubber or nitrile) coated with four levels (high, medium, low or none) organic matter after touching contaminated soil or lettuce. 

Objective 6. Determine the likelihood and degree of pathogen (E. coli O157:H7, Salmonella and norovirus) transfer that occurs when contaminated gloves (rubber or nitrile), also treated with four degrees of organic matter (high, medium, low and none), touch a single head of lettuce and determine how many additional lettuce heads can become contaminated if touched following a single glove contamination event.

Objective 7. Optimize the formulation of a levulinic acid plus SDS sanitizing solution for maximal removal of organic material and inactivation of pathogens (E. coli O157:H7, Salmonella and norovirus) on one glove type (rubber or nitrile) and compare the efficacies to that of a bleach sanitizer for gloves. 

Objective 8. Define the maximal organic/soil load that can be present on gloves or in sanitizing solution buckets (placed in the field for purpose of rinsing gloves) without diminishing efficacy of removing organic material or inactivating pathogens(E. coli O157:H7, Salmonella and norovirus).

Preventing cross-contamination by norovirus: Noroviruses are not known to be zoonotic pathogens. The control point for preventing cross-contamination is at the point where gloves are applied. Contaminated irrigation water is another potential concern, but unless the water is contaminated with raw human sewage, contamination of produce is suspected to occur with very little frequency and with very low levels of contamination. Alternatively, high levels of norovirus can be excreted from infected persons, both when symptomatic (up to 1012 viruses per gram of feces) and when asymptomatic (up to 109 viruses per gram of feces) (1). If strict hand hygiene is not followed after restroom use, we demonstrated that high levels of virus could be transferred to gloves when gloves are applied; the primary site of this contamination would be on the wrists of the gloves if gloves are applied properly. Our study also demonstrates that norovirus contamination on gloves can be reduced by disinfection of glove surfaces. Using waterless hand sanitizers (Purell or 5% levulinic acid plus 2% SDS foam) on gloves, infectious noroviruses can be reduced by ~1-2 log PFU. Using 50 ppm chlorine with a single glove-dunk bucket, similar levels of norovirus disinfection on latex and Canner’s gloves could be achieved, but higher reductions in infectious virus (~3-4 log PFU) can be obtained when nitrile gloves are treated. Preventing cross-contamination by bacterial pathogens: The primary route of crosscontamination by bacterial pathogens is likely to be in the field. Encounters of high levels of contamination in the harvest environment are low frequency occurrences, but if encountered, contamination of product can be amplified by handler cross-contamination. Our studies demonstrate that viable bacterial pathogens on gloves can be significantly reduced after glovedunk buckets containing chlorine concentrations of at least 50 ppm (pH 7). When contamination levels are low (≤ 3 CFU/glove), complete inactivation can be achieved; if high levels of glove contamination occur, we have demonstrated 4-6 log CFU reductions on gloves, but complete inactivation was not always achieved, especially in the case of nitrile gloves. Alternative sanitizers can also be used to reduce pathogen contamination, but the lower efficacy of Purell and the high cost of levulinic acid plus SDS make these alternatives less attractive. Taken together, we make the following recommendations: Strict hand hygiene is imperative prior to glove application. To minimize contamination by noroviruses we recommend disinfecting gloves in a chlorine (at least 50 ppm; pH 7) glove-dunk bucket after each time gloves are applied. Alternatively, or in addition, consider double-gloving or wearing glove liners. [Note: if non-disposable glove liners are worn, they should be laundered under sanitizing conditions (hot water) each day after use.] To minimize contamination by bacterial pathogens, gloves should be disinfected in chlorine (at least 50 ppm; pH 7) glove-dunk buckets before beginning work, before each break or lunch period, and when returning back to work after each break or lunch period. Gloves should be rubbed aggressively, palms-together for 5-10 seconds while gloved hands are immersed up to the wrist in the bucket. Sponges, brushes, or any other type of mildly abrasive cleaning aid should not be used with glove-dunk buckets. Free chlorine and pH should be measured and maintained above 50 ppm and neutral pH in the glove-dunk buckets. Measurements should be taken before use and the buckets should be covered when not in use to prevent chlorine dissipation. Buckets may need to be refreshed after each break period, especially when latex gloves are used or if lettuce or soil debris begins to accumulate. Gloves should not be taken home by employees (cannot control what the gloves will be used for at home). Disposable gloves should be discarded at the end of each day of use.