Typhoid fever is contracted by the ingestion of the bacteria in contaminated food or water. Patients with acute illness can contaminate the surrounding water supply through stool, which contains a high concentration of the bacteria. Contamination of the water supply can, in turn, taint the food supply. About 3%-5% of patients become carriers of the bacteria after the acute illness. Some patients suffer a very mild illness that goes unrecognized. These patients can become long-term carriers of the bacteria. The bacteria multiplies in the gallbladder, bile ducts, or liver and passes into the bowel. The bacteria can survive for weeks in water or dried sewage. These chronic carriers may have no symptoms and can be the source of new outbreaks of typhoid fever for many years.
How does the bacteria cause disease, and how is it diagnosed?
After the ingestion of contaminated food or water, the Salmonella bacteria invade the small intestine and enter the bloodstream temporarily. The bacteria are carried by white blood cells in the liver, spleen, and bone marrow. The bacteria then multiply in the cells of these organs and reenter the bloodstream. Patients develop symptoms, including fever, when the organism reenters the bloodstream. Bacteria invade the gallbladder, biliary system, and the lymphatic tissue of the bowel. Here, they multiply in high numbers. The bacteria pass into the intestinal tract and can be identified for diagnosis in cultures from the stool tested in the laboratory. Stool cultures are sensitive in the early and late stages of the disease but often must be supplemented with blood cultures to make the definite diagnosis.