Estimates on reduction of disease incidence can be provided as a means of establishing possible payback periods in terms of illness time, insurance, and employee morbidity. Since immune buildings will control airborne microbes, reduced disease incidence from everyday respiratory infections is a distinct possibility. Although no data is currently available that would allow extrapolation of such cost savings, estimates can be made based on company records. These estimates can be compared with actual employee illness records subsequent to the installation of any immune building systems to verify either the effectiveness or the cost savings.