Table 1.
Model parameter inputs and distributions.
| Parameter | Units | Description | Distribution | Input Values | Type of Variability/Uncertainty | Citations |
|---|---|---|---|---|---|---|
|
Viral Shedding |
||||||
| Log10(Cvirus) | PFU/mL | Concentration of virus in saliva | Triangular | 6.8 (6.1, 7.4) | Variability and parameter uncertainty | (To et al., 2020; Wolfel et al., 2020) |
| 100X increased viral shedding | 8.8 (8.1, 9.4) | |||||
| 10X increased viral shedding | 7.8 (7.1, 8.4) | |||||
| 2X increased viral shedding | 7.1 (6.4, 7.7) | |||||
| VF,c | mL/Cough | Fraction of volume associated with aerosols (2–45 μm) | Triangular | 2.3 × 10−6 (1.4 × 10−6, 2.6 × 10−6) | Variability and parameter uncertainty | Chao et al. (2009) |
| VF,c | mL/Cough | Fraction of volume associated with droplets (50–60 μm) | Triangular | 6.0 × 10−6 (3.5 × 10−6, 6.7 × 10−6) | Variability and parameter uncertainty | Chao et al. (2009) |
| VF,c | mL/Cough | Fraction of volume associated with droplets (60–100 μm) | Triangular | 4.9 × 10−6 (1.1 × 10−6, 8.4 × 10−6) | Variability and parameter uncertainty | Chao et al. (2009) |
| VF,c | mL/Cough | Fraction of volume associated with droplets (100–750 μm) | Triangular | 6.8 × 10−3 (4.0 × 10−3, 7.6 × 10−3) | Variability and parameter uncertainty | Chao et al. (2009) |
| FC | Cough/h | Number of coughs per hour | Empirical | 1/11 equal probability (0, 10) | Variability and parameter uncertainty | (Adhikari et al., 2019; Loudon & Roberts, 1967) |
| λvirus | Hour | Aerosol viral decay of SARS-CoV-2 at 40% relative humidity, 38 °F | Point value | 0 | Fixed parameter | (DHS, 2021a) |
| pp | Probability | Probability respiratory particles will remain in the air as respiratory spray between 0 and 1m distancing | Uniform | 50–60 μm: | Assumption uncertainty | Bourouiba et al. (2014) |
| 1m: 0.82; | ||||||
| 60–100 μm: | ||||||
| 1m: 0.44; | ||||||
| >100 μm: | ||||||
| 1m: 0.04 | ||||||
| ppdroplets | Probability | Probability respiratory particles (>100 μm) will remain in the air as respiratory spray between 0 and 1m distancing | Uniform | (0.01, 0.22) | Assumption uncertainty | Bourouiba et al. (2014) |
| ppfalldroplets |
Probability |
Probability respiratory particles (>100 μm) will settle to the fomite surfaces between 0 and 1m distancing |
Uniform |
(0.07, 0.78) |
Assumption uncertainty |
Bourouiba et al. (2014) |
|
Risk Mitigation Interventions1 |
||||||
| Smask | Log reduction | Source protection surgical mask efficacy | Uniform | (0.39, 0.57) | Variability | (Lindsley et al., 2021; Maurer et al., 2021; Ueki et al., 2020) |
| RSmask | Percent reduction | Recipient surgical mask efficacy | Uniform | (0.37, 0.998) | Variability | (Lindsley et al., 2021; Maurer et al., 2021; Ueki et al., 2020) |
| SDeff | Log reduction | Plastic fomite surface decontamination efficiency | Point value | 3 Log10 virus | Fixed parameter | (EPA, 2020; Malenovska, 2020) |
| HWeff | Log reduction | Handwashing efficiency | Point value | 2 Log10 virus | Fixed parameter | (Grove et al., 2006; Liu et al., 2010) |
| HWfreq | Handwashing/h | Frequency of handwashing per hour | Point value | 1.0 | Fixed parameter | Expert elicitation |
| Rair | Air changes/h | Frequency of room air changes per hour (ACH) | Point value | 2.0 | Fixed parameter | Expert elicitation |
| VEoptimal | Percent reduction | Vaccine effectiveness (VE) | Uniform | (0.86, 0.99) | Variability | (Andrejko et al., 2021; Pawlowski et al., 2021; Swift et al., 2021) |
| VEreduced | Percent reduction | Vaccine effectiveness (VE) | Uniform | (0.64, 0.80) | Variability | (Khan & Mahmud, 2021; Moustsen-Helms et al., 2021) |
| VET |
Percent reduction |
Vaccine effectiveness against transmission (VET) |
Triangular |
0.89 (0.82, 0.95) |
Variability |
Prunas et al. (2021) |
|
Fomite-Mediated Transmission |
||||||
| SAcarton.top | m2 | Surface area of top of individual plastic carton | Uniform | (0.106, 0.116) | Variability and parameter uncertainty | Assumed |
| SAcarton | m2 | Surface area of a single individual plastic carton | Uniform | (0.41, 0.54) | Variability and parameter uncertainty | Assumed |
| Cartons | Cartons/h | Number of individual plastic cartons processed per h | Uniform | (144, 216) | Variability and parameter uncertainty | Assumed |
| Pallets | Pallets/h | Number of pallets processed per h | Point value | 4.0 | Fixed parameter | Assumed |
| SAplasticwrap.side | m2 | Surface area of a single side of plastic wrapped pallet | Uniform | (4.20, 6.97) | Variability and parameter uncertainty | Assumed |
| SAplasticwrap | m2 | Surface area of entire plastic wrapped pallet | Uniform | (25.2, 41.8) | Variability and parameter uncertainty | Assumed |
| Fingerssa | m2 | Surface area of three finger tips touching the surface | Point value | 0.00042 | Fixed parameter | Bouwknegt et al. (2015) |
| Hsa | m2 | Area of two hands (palms only) | Point value | 0.049 | Fixed parameter | Bouwknegt et al. (2015) |
| decay.time | Days | Transport time between the frozen food manufacturing facility and the receiving warehouse (days) | Uniform | (30, 90) | Variability | Assumed |
| Fdecay | Days−1 | Viral decay rate (PFU per day) | Uniform | (0.14, 0.22) | Variability | Kwon et al. (2021) |
| TEfh | PFU | Viral transfer fraction from fomite to hand with relative humidity (15–32%); acrylic surface 2 | Triangular | 0.217 (0.067, 0.367) | Variability and parameter uncertainty | Lopez et al. (2013) |
| TEhf | PFU | Viral transfer fraction from hand to fomite surface | Point value | 0.025 | Fixed parameter | (Bean et al., 1982; Greene et al., 2015; Nicas & Jones, 2009; Rusin et al., 2002) |
| TEhm | PFU | Viral transfer fraction from hand to face | Triangular | 0.200 (0.137, 0.263) | Variability and parameter uncertainty | Lopez et al. (2013) |
| freq.hs | Contacts/min | Frequency of contacts from hand to individual plastic cartons | Point value | Cartons/60 | Fixed parameter | Assumed |
| freq.hs.pw | Contacts/min | Frequency of contacts from hand to plastic wrap | Uniform | (4/60, 20/60) | Variability and parameter uncertainty | Assumed |
| freq.hf | Contacts/min | Frequency of contacts from hand to face | Point value | 0.80 | Variability and parameter uncertainty | Nicas and Best (2008) |
| Handdecay | Minutes | Viral decay rate on hands (PFU/min) | Uniform | (0.92, 1.47) | Variability | Nicas and Jones (2009) |
| eyes.sa | m2 | Surface area of mucous membranes—eyes | Uniform | (1 × 10−5, 2 × 10−4) | Variability | Wilson et al. (2018) |
| nose.sa | m2 | Surface area of mucous membranes—nose | Uniform | (1 × 10−5, 1 × 10−3) | Variability | Wilson et al. (2018) |
| mouth.sa |
m2 |
Surface area of mucous membranes—mouth |
Uniform |
(1 × 10−4, 4.1 × 10−3) |
Variability |
Wilson et al. (2018) |
|
SARS-CoV-2 Dose and Risk Characterization |
||||||
| Ratioinfectious | No units | Infectious to non-infectious ratio | Point value | 1:100 | Fixed parameter | Pitol and Julian (2021) |
| krisk | PFU−1 | Dose-response parameter | Point value | 0.00680 | Fixed parameter | Pitol and Julian (2021) |
Note.1All interventions were assumed to be implemented with 100% compliance. 2Fomite-to-hand transfer rate derived from laboratory studies with bacteriophage MS2.