Requisites for the Transmission of Pathogenic Organisms

Infection is the invasion and multiplication of microorganisms in body tissues resulting in local cellular injury as a consequence of competitive metabolism, toxin production, and immune-mediated reactions. The “chain of infection,” i.e., the transmission of pathogenic organisms in any setting requires three elements: (1) a source or reservoir of infectious agents, (2) a susceptible host with a portal of entry receptive to that agent, and (3) a mode of transmission for the agent.¹