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Typhoid Fever

What is typhoid fever?

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, when tens of thousands of cases were reported in the U.S. Today, less than 400 cases are reported annually in the United States, mostly in people who have recently traveled to Mexico and South America. This improvement is the result of better environmental sanitation. India, Pakistan, and Egypt are also known as high-risk areas for developing this disease. Worldwide, typhoid fever affects more than 21 million people annually, with about 200,000 people dying from the disease.

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How Do People Get Typhoid Fever?

Typhoid fever is contracted by drinking or eating the bacteria in contaminated food or water. People 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. The bacteria can survive for weeks in water or dried sewage.

About 3%-5% of people become carriers of the bacteria after the acute illness. Others suffer a very mild illness that goes unrecognized. These people may become long-term carriers of the bacteria -- even though they have no symptoms -- and be the source of new outbreaks of typhoid fever for many years.

How Is Typhoid Fever 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, where they multiply and reenter the bloodstream. People develop symptoms, including fever, at this point. 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 in stool samples. If a test result isn't clear, blood samples will be taken to make a diagnosis.

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