Final answer:
Genetic factors, environmental factors, and microbial factors account for the variation in symptoms and severity of CDI.
Step-by-step explanation:
The variation in symptoms and severity of C. difficile infection (CDI) is influenced by several factors, including genetic factors, environmental factors, and microbial factors. Genetic factors refer to individual variations in genes that can affect susceptibility to the infection or the body's ability to respond to it. Environmental factors such as exposure to certain substances or conditions can also play a role in determining the severity of CDI. Lastly, microbial factors, including the particular strain of C. difficile involved, can contribute to the variation in symptoms and severity.