Final answer:
The extent of host involvement in the initial infection is determined by a complex relationship between the microorganism's virulence factors and the immune defenses of the individual.
Step-by-step explanation:
The extent of host involvement in the initial infection is determined by a complex relationship between the microorganism's virulence factors and the immune defenses of the individual. Factors such as preexisting conditions, environmental factors, and genetically determined immune factors can make individuals more or less susceptible to infection. These host factors interact with the pathogenicity factors produced by the microorganism to determine the outcome of the infection.