Equations describing the loading of microbes on hands (directly or through an object) and the transfer of microbes from hand-to-mouth were used to determine the final dose for each exposure scenario (Zartarian et al. 2000). Model parameters are presented in Table 1 for the hand contamination distributions and Table 2 for the dose distributions. Model parameters and equations are described further in the Appendix (available with the online version of this paper).
Model parameters used to estimate hand and object contamination distributions
| Variable . | Symbol . | Parameter . | Source . |
|---|---|---|---|
| Microbe concentration (log10/100 mL) | |||
| Coliphage | CC | Normal (5.56, 1.18) | This study |
| E. coli | CEc | Normal (8.60, 1.00) | This study |
| Time spent in the drain per entry event (hr) | |||
| Deliberate entry | TD | Determined from a hazard model of children's activities | This study |
| Frequency of contact with drain (#/drain entry event) | |||
| Accidental entry | DA | Poisson (1) | Assumption |
| Incidental entry | DI | Poisson (1) | Assumption |
| Deliberate entry | DD | Poisson (5×TD) | Assumption |
| Area of surface (cm2) | |||
| Hands, young childrena | AY | Uniform (244.4, 329.0) | US EPA (2011) |
| Hands, older childrenb | AM | Uniform (380.7, 695.6) | US EPA (2011) |
| Object | AO | Uniform (378.8, 1515.5) | Assumption |
| Object contacted (%) | |||
| Hand in drain water | SHDW | Uniform (0.08, 1.00) | AuYeung et al. (2008) |
| Object in drain water | SODW | Uniform (0.25, 1.00) | Assumption |
| Hand on object | SOH | Uniform (0.08, 0.27) | AuYeung et al. (2008) |
| Water film thickness (cm) | |||
| Hand or object | V | Uniform (0.00241, 0.00499) | US EPA (1987) |
| Transfer efficiency, object to hand (%) | |||
| Coliphage | TEOC | 0.2759 | Rusin et al. (2002) |
| E. coli | TEOEc | 0.6580 | Rusin et al. (2002) |
| Variable . | Symbol . | Parameter . | Source . |
|---|---|---|---|
| Microbe concentration (log10/100 mL) | |||
| Coliphage | CC | Normal (5.56, 1.18) | This study |
| E. coli | CEc | Normal (8.60, 1.00) | This study |
| Time spent in the drain per entry event (hr) | |||
| Deliberate entry | TD | Determined from a hazard model of children's activities | This study |
| Frequency of contact with drain (#/drain entry event) | |||
| Accidental entry | DA | Poisson (1) | Assumption |
| Incidental entry | DI | Poisson (1) | Assumption |
| Deliberate entry | DD | Poisson (5×TD) | Assumption |
| Area of surface (cm2) | |||
| Hands, young childrena | AY | Uniform (244.4, 329.0) | US EPA (2011) |
| Hands, older childrenb | AM | Uniform (380.7, 695.6) | US EPA (2011) |
| Object | AO | Uniform (378.8, 1515.5) | Assumption |
| Object contacted (%) | |||
| Hand in drain water | SHDW | Uniform (0.08, 1.00) | AuYeung et al. (2008) |
| Object in drain water | SODW | Uniform (0.25, 1.00) | Assumption |
| Hand on object | SOH | Uniform (0.08, 0.27) | AuYeung et al. (2008) |
| Water film thickness (cm) | |||
| Hand or object | V | Uniform (0.00241, 0.00499) | US EPA (1987) |
| Transfer efficiency, object to hand (%) | |||
| Coliphage | TEOC | 0.2759 | Rusin et al. (2002) |
| E. coli | TEOEc | 0.6580 | Rusin et al. (2002) |
aChildren aged less than 5 years.
bChildren aged 5–12 years.
Model parameters used to estimate dose distributions
| Variable . | Symbol . | Parameter . | Source . |
|---|---|---|---|
| Object contacted (%) | |||
| Hand in mouth | SHM | Uniform (0.06, 0.33) | AuYeung et al. (2007) |
| Frequency of hand mouthing (#/hour) | |||
| Young childrena | HMY | Weibull (0.56, 3.41) | Xue et al. (2007) |
| Older childrenb | HMM | Weibull (0.49, 1.47) | Xue et al. (2007) |
| Time microbes could be ingested (hours) | |||
| Time to hand washing | THW | Uniform (0.05, 4.10) | Freeman et al. (2001) |
| Transfer efficiency, hand to mouth (%) | |||
| Coliphage | TEHC | 0.3390 | Rusin et al. (2002) |
| E. coli | TEHEc | 0.3397 | Rusin et al. (2002) |
| Variable . | Symbol . | Parameter . | Source . |
|---|---|---|---|
| Object contacted (%) | |||
| Hand in mouth | SHM | Uniform (0.06, 0.33) | AuYeung et al. (2007) |
| Frequency of hand mouthing (#/hour) | |||
| Young childrena | HMY | Weibull (0.56, 3.41) | Xue et al. (2007) |
| Older childrenb | HMM | Weibull (0.49, 1.47) | Xue et al. (2007) |
| Time microbes could be ingested (hours) | |||
| Time to hand washing | THW | Uniform (0.05, 4.10) | Freeman et al. (2001) |
| Transfer efficiency, hand to mouth (%) | |||
| Coliphage | TEHC | 0.3390 | Rusin et al. (2002) |
| E. coli | TEHEc | 0.3397 | Rusin et al. (2002) |
aChildren aged less than 5 years.
bChildren aged 5–12 years.