Which intrinsic factor can affect a host's susceptibility to infection?

The age of the host is a significant intrinsic factor that can affect susceptibility to infection. Various age groups experience different immune responses, with infants and the elderly typically being more vulnerable. In young children, the immune system is still developing and may not effectively combat pathogens. Conversely, in older adults, the immune system may be waning or less responsive due to natural aging processes, making them more susceptible to infections. Additionally, age-related physiological changes can affect the body's ability to respond to infections, making it essential to consider when assessing the risk of infectious diseases.

The other factors mentioned—socioeconomic status, access to clean water, and quality of healthcare—while crucial in understanding overall health and disease prevention, are primarily external factors. They relate to the environment and public health infrastructure rather than being inherent characteristics of the individual host. Hence, age stands out as a directly intrinsic factor linked to the host's biological and immunological conditions.