Table 1.
Parameters, values, and probability distributions used in the QMRA models.
| Variable Notation | Definition [units] | Distribution and/or Values | References |
|---|---|---|---|
|
| |||
| Inputs associated with norovirus viral load and contamination of hands by fecal matter | |||
| conc/concp | Concentration of norovirus in stool – harvester and packer [virions/gram] | 10BetaPert (2,6,11); min: 100, mode: 1,000,000, max: 100,000,000,000 (shape = 10) | (Atmar et al., 2014; Kirby et al., 2014; Mokhtari and Jaykus, 2009) |
| mfh/mfhp | Mass of feces/hand—harvester and packer [grams/hand] | Generalized beta: shape1: 4.57, shape2: 2.55, min: −8.00, max: −1.00 | (Bouwknegt et al., 2015) |
| Inputs associated with farmworker health and hygiene behavior (handwashing compliance and efficacy, glove use) | |||
| hweff/hweffp | Handwashing removal efficacy— harvester and packer [log10 virions] | Triangle (0.0, 0.5, 6) | (Doultree et al., 1999; Duizer et al., 2004; Grove et al., 2015; Kampf et al., 2005; Kramer et al., 2006; Lages et al., 2008; Liu et al., 2010; Macinga et al., 2008; Mokhtari and Jaykus, 2009; Sattar, 2002; Tuladhar, 2015) |
| Phhw/Pphw | Probability of handwashing— harvester and packer [%] | Empirical (0.27,0.73) | (Green et al., 2006) |
| Phwg/Ppwg | Probability of using gloves— harvester and packer [%] | Empirical (0.25,0.75) | (Emery, 1990; FDA, 2000; Green et al., 2006; Michaels and Ayers, 2002; Michaels et al., 2004; Mokhtari and Jaykus, 2009) |
| prev | Community-based asymptomatic norovirus prevalence among adults — harvester and packer [%] | Empirical (0.04,0.96) | (Qi et al., 2018) |
| Inputs associated with tactile contacts during harvesting and packing | |||
| Trhhp/Trphp | Proportion of norovirus transfer per touch from bare hands to produce— harvester and packer: | ||
| Lettuce | Uniform (0.123, 0.237) | (Bidawid et al., 2004) | |
| Tomato | Log Normal: mean log: −2.22, SD log: −0.17 | (Tuladhar et al., 2013) | |
| Raspberry | Log Normal: mean log: −2.32, SD log: −0.15 | (Bouwknegt et al., 2015) | |
| Trhgp/Trpgp | Proportion of norovirus transfer per touch from gloved hands to produce— harvester and packer | Beta, shape 1: 1.165, shape 2: 2.630 | (Barker et al., 2004; Bidawid et al., 2004; Mokhtari and Jaykus, 2009) |
| Trpph | Proportion of norovirus transfer per touch from produce to bare hands— packer only: | (Bidawid et al., 2004; Bouwknegt et al., 2015; Verhaelen et al., 2013) | |
| Lettuce | Uniform (0.105, 0.175) | ||
| Tomato | Uniform (0.105, 0.175) | ||
| Raspberry | Beta, shape 1: 7.42, shape 2: 39.51 | ||
| Trhpbi | Proportion of norovirus transfer per touch from produce to bin | Triangle (0.009,0.028, 0.038) | (D’Souza et al., 2006; Escudero et al., 2012; Stals, 2013; Stals et al., 2015) |
| Trppbe | Proportion of norovirus transfer per touch from packing produce to belt | Triangle (0.009,0.028, 0.038) | (D’Souza et al., 2006; Escudero et al., 2012; Stals, 2013; Stals et al., 2015) |
| Trhhg/Trphg | Proportion of norovirus transfer per touch from contaminated bare hand /restroom environment to glove— harvester and packer | Uniform (0,0.444) | (Ronnqvist et al., 2014) |
| Trhppbi | Proportion of produce to produce norovirus transfer per contact in harvest bin | Beta, shape 1: 2.257, shape 2: 15.502 | (Barker et al., 2004; Bidawid et al., 2004; Mokhtari and Jaykus, 2009) |
| nhPh/npPh | Number of hand-to-produce contacts—harvester and packer | Empirical (1), p(1) | Assumption |
| nPbi | Number of produce-bin contacts | Empirical (1–5), p(0.2,0.2,0.2,0.2,0.2) | Assumption |
| nPbe | Number of produce-belt contacts | Empirical (1–5), p(0.2,0.2,0.2,0.2,0.2) | Assumption |
| nPPbi | Number of produce-to-produce contacts in bin | Empirical (1–10), p(0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1, 0.1) | Assumption |
| norodecay | Norovirus log10 reduction per day at: Lettuce: 5°C Tomato, raspberry: 20°C |
Point (0.011) Point (0.151) |
(Bouwknegt et al., 2015) |
| Inputs associated with dose-response, exposure assessment, and risk characterization for the consumer | |||
| μ | Mean aggregate size | Triangle (399, 1106, 2428) | (Messner et al., 2014) |
| P | Dose-response: probability of infection among susceptible subjects | Triangle (0.63, 0.722, 0.8) | (Messner et al., 2014) |
| bodyweight | Adult body weight [kilograms] | Point (80) | (EPA, 2011) |
| weightlettucehead | Reported weight per single raw lettuce head (representing red leaf, green leaf, and romaine lettuces) [grams] | Triangle (309, 360, 626) | (U.S. Department of Agriculture, Agricultural Research Service, 2019) |
| weighttomato | Reported weight per single tomato [grams] | Triangle (91, 123, 182) | (U.S. Department of Agriculture, Agricultural Research Service, 2019) |
| weightberry | Reported weight per single raspberry [grams] | Triangle (3, 4, 5) | (U.S. Department of Agriculture, Agricultural Research Service, 2019) |
| lettuceconsumpt | Consumer-Only 2-Day average intake of lettuce, whole population [g/kg-day] | Normal 0.44, SD: 0.01 | (EPA., 2018) |
| tomatoconsumpt | Consumer-Only 2-Day average intake of tomatoes, whole population [g/kg-day] | Normal 0.83, SD: 0.02 | (EPA., 2018) |
| berryconsumpt | Consumer-Only 2-Day average intake of berries, whole population [g/kg-day] | Normal 0.45, SD: 0.02 | (EPA., 2018) |