Conceptual model.

The top half of the diagram shows the observed yearly disease incidence. The bottom half of the diagram illustrates the infected patient (patients lying on beds to the left) and the route of infected excretion products via flies or polluted irrigation water and infected vegetables to susceptible individuals (standing persons on right) who become further infected individuals (lying on beds). Disease transmission mechanisms (bottom part of image) and observations (top) suggest study hypotheses involving disease sources and factors (x), transmissions (y∼x), and spatiotemporal patterns (y).