Topic overview

Start with the big picture

This topic introduces infection as microbial invasion and multiplication accompanied by a host response, while distinguishing it from colonization without tissue damage. It outlines a chain of infection, from entry and adherence through multiplication, damage, and exit, and explains how reservoirs and portals shape transmission. Modes covered include direct and indirect contact, droplet and airborne spread, common vehicles, vectors, zoonoses, vertical transmission, and healthcare-associated sources. The lesson also introduces epidemiological concepts such as incubation periods and reproductive number, then connects transmission routes to infection-control precautions. Together, these ideas help organize how pathogens spread and where control measures can interrupt that spread.