This is a schematic of invasion of Salmonella through the small intestines.

Salmonella tend to adhere and colonize this part of the intestine, and can spend several days multiplying, and slowly penetrating into the columnar cells and the Peyers Patches, which are collections of lymphoid tissue in the intestines. Indeed, S. typhi typically has a 10 –14 day incubation period, i.e. a 10 – 14 day delay between ingestion of the organism, and development of signs and symptoms of illness. During this 10 – 14 days this process or replication, adherence, and penetration steadily progresses.

S. Typhi can live and reproduce within the phagocytic cells of human immune system. These immune cells circulate throughout the body, and so they provide a way for the bacteria to gain access to the blood stream and circulate throughout the body.