Biological Basis of Infectious Disease Epidemiology

Abstract An understanding of infectious disease epidemiology cannot be distilled to a discussion of an infectious agent inflicting disease on susceptible human hosts. Although understanding infectious pathogens is important, other factors involving the host and the environment contribute to the transmission of infectious agents, disease production, and the outcome of an infection. Infection represents a complex interplay between host factors, characteristics of the infectious agent, and environmental influences. This complex interaction has been modeled as a triangle (Jackson 1996) (Fig. 1-1), a wheel (Fig. 1-2, Jackson 1996), a tetrahedron (Fig. 1-3) (Rothenberg 1990), or a chain (Fig. 1-4) (Jackson 1996). Regardless of which model one uses to describe the interaction of humans with infectious agents and their environment, a person’s state of health represents a dynamic equilibrium-a balance of forces.