Ace the VCDH Microbiology Challenge 2026 – Dive Deep and Discover Your Inner Scientist!

Infectivity refers to the ability of a pathogen to establish an infection in a host after exposure. It measures how readily the organism can begin an infection, needing to attach, invade, and begin replication while overcoming host defenses. This is about initiating infection, not how often infections occur in a population—that would be the rate of infection. It’s also distinct from virulence, which describes how severe disease is once infection is established, and from pathogenicity, which is the broader capacity to cause disease overall. So the best phrasing captures the concept as the organism’s capacity to infect.