Table 1.
Parameter descriptions for simulations of the Skagit County, WA March 2020 SARS-CoV-2 transmission case study. *Simulated worlds were 10 m × 18 m. †Standard deviations are given in parentheses. ‡Zero-percent mask efficacy is equivalent to no mask use. §Das et al. (2020) estimated the average travel distance of a 100-micrometer droplet expelled from a height of 1.7 m at a velocity of 0.5 m/s to be 0.55 m. They also found that the majority of 100-μm droplets will fall 0.55–2.35 m away from the expelling individual, depending on initial velocity, but droplets may settle up to 3.2 m away very rarely. a random draw of 10,000,000 samples from a log-normal distribution parameterized using 1.7-m and 0.2095-m droplet spread distance mean and standard deviation values, respectively, generated a distribution in line with this finding. The standard deviation we use in simulations for non-coughing expectoration is proportionate to the one used in this random draw.
| Parameter/Model Input | Value (s) | Reference (s) |
|---|---|---|
| Infectiousness parameters | ||
| Cough frequency (coughs/min) | 0.19 | Lee et al., 2012 |
| Droplet count (droplets/expectoration) | 9.7e5 (3.9e5)† | Miller et al., 2020, Appendix S2 |
| Droplet spread angle – coughing (º) | 35 | Kwon et al., 2012 |
| Droplet spread angle – not coughing (º) | 63.5 | Kwon et al., 2012 |
| Droplet travel distance – coughing (m) | 5 (0.256)† | Bourouiba et al., 2014 |
| Droplet travel distance – not coughing (m) | 0.55 (0.068)†§ | Das et al., 2020 |
| Scenario environment and individual behavior inputs | ||
| Area (m2) | 180* | Hamner et al., 2020 |
| Expectoration height (m) | 1.7 | Fryar et al.m, 2018 |
| Inhalation rate (m3 air/min) | 0.023 | Adams, 1993 |
| Maximum people in a single 1-m2 patch (people) | 2 | Hamner et al., 2020 |
| Number of symptomatic individuals (people) | 1 | Hamner et al., 2020 |
| Scenario virion behavior inputs | ||
| Virion count (virions/mL fluid) | 2.35e9 | Wölfel et al., 2020 |
| Virion decay rate (%/min) | 1.05 | van Doremalen et al., 2020 |
| Virion infection risk (%/inhaled virion) | 6.24 | Appendix S2 |
| Scenario airflow inputs | ||
| Diffusion rate (m3/min) | 1.5e-3 | Castillo and Weibel, 2018 |
| Forced air | on, off | – |
| Forced air direction | North-to-South, East-to-West | – |
| Air change rate (%/min) | 4.3 | Miller et al., 2020 |
| Re-circulated air filtration (%/min) | 90 | Miller et al., 2020 |
| Scenario intervention inputs | ||
| Attempted social distancing (m) | 0, 1, 2, 3 | – |
| Contact duration (min) | 20, 40, 60, 90, 105, 150 | – |
| Mask efficacy (%) | 0‡, 25, 50, 75, 90 | Jefferson et al., 2008;Asadi et al., 2020 |
| Population (people) | 10, 50, 61 | – |