Before revision:  In addition, the reduction in transmission associated with physical distancing between the host and susceptible as well as the level of physical activity  of the host and /or the susceptible in enhancing transmission risk, is also examined .
After revision:  In addition, the reduction in transmission associated with physical distancing between the host and susceptible is also quantified by coupling the model with available data on scalar dispersion in canonical flows. Finally, the effect of the level of physical activity of the host and /or the susceptible in enhancing transmission risk, is also examined .