Salmonella Typhi causes typhoid fever, a serious infection spread through contaminated food or water.
Unlike most Salmonella infections, which commonly cause gastroenteritis, S. Typhi is adapted to humans and can invade the bloodstream. It is transmitted by the fecal–oral route, especially where sanitation and access to clean water are limited. Some infected people become chronic carriers, with the bacteria persisting in the gallbladder.
Typhoid fever is not the same as typhus, which is caused by several Rickettsia species and is usually spread by arthropods. Typhoid vaccination, safe water, handwashing, and appropriate antibiotic treatment help control the disease. Antibiotic resistance has complicated treatment in some regions, making laboratory testing increasingly important.
The bacterium is classified as Salmonella enterica serovar Typhi; “Salmonella Typhi” is the standard short form. Related serovars such as Paratyphi cause paratyphoid fever, a similar but distinct illness.