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| Variable | Description | Unit |
| S | Susceptible individual density | Individuals·km−2 |
| E | Exposed individual density | Individuals·km−2 |
| I | Infectious individual density | Individuals·km−2 |
| A | Asymptomatic individual density | Individuals·km−2 |
| R | Recovered/removed individual density | Individuals·km−2 |
| N | Total population density | Individuals·km−2 |
| W | Pathogen concentration in water reservoir | Cells·mL−3 |
