Typhoid fever is an acute illness associated with fever caused by the Salmonella typhi bacteria. It can also be caused by Salmonella paratyphi, a related bacterium that usually causes a less severe illness. The bacteria are deposited in water or food by a human carrier and are then spread to other people in the area. The incidence of typhoid fever in the United States has markedly decreased since the early 1900s. Today, less than 500 cases are reported annually in the United States, mostly in people who recently have traveled to endemic areas. This is in comparison to the 1920s, when over 35,000 cases were reported in the U.S. This improvement is the result of improved environmental sanitation. Mexico and South America are the most common areas for U.S. citizens to contract typhoid fever. India, Pakistan, and Egypt are also known high-risk areas for developing this disease. Worldwide, typhoid fever affects more than 13 million people annually, with over 500,000 patients dying of the disease. How do patients get typhoid fever? 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 need to be supplemented with blood cultures to make the definite diagnosis.
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