What does "transmission" refer to in infectious diseases?

Transmission in the context of infectious diseases refers specifically to the spread of a disease from one host to another. This process can occur through various routes, such as direct contact, airborne particles, vector-borne means (like mosquitoes), or through contaminated surfaces. Understanding transmission is crucial for disease control and prevention strategies, as it helps identify how infections propagate and can inform measures to reduce their spread.

The other options touch on related concepts but do not accurately define transmission. For instance, the decay rate of infectious agents outside a host pertains to the stability and viability of the pathogens in the environment rather than their movement between hosts. The immune response is more concerned with how the body reacts to an infection rather than how the infection is spread. Prevention strategies, while essential in managing diseases, focus on mitigating transmission but do not define what transmission itself is. Therefore, recognizing that "transmission" specifically indicates the movement of pathogens between hosts clarifies the key dynamics of infectious disease spread.