What key factor does NOT contribute to the determination of infection susceptibility?

The correct answer emphasizes that the risk level of the organism does not directly contribute to determining the susceptibility of an individual to infection. Infection susceptibility is typically more dependent on the host factors, such as the individual's age, overall health status, and the manner in which they were exposed to the pathogen.

Understanding infection susceptibility requires focusing on how a person's body responds to potential infectious agents rather than the characteristics of the pathogens themselves. For example, younger individuals, older adults, or those with compromised immune systems may be more susceptible to infections due to biological vulnerabilities, regardless of how dangerous a given organism is perceived to be. The overall health status plays a crucial role in immunity; individuals with pre-existing medical conditions may have a reduced ability to fend off infections.

Furthermore, the method of exposure is significant; how a person is exposed to an infectious agent can influence whether or not they become infected. In contrast, the inherent risk level of the organism—such as its virulence or resistance to treatment—does not alter the individual’s susceptibility but rather reflects the threat that the organism poses in a broader demographic context. Thus, this option stands out as unrelated to the personal factors that affect an individual's likelihood of infection.