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Typhoid and paratyphoid fever are caused by infection with the bacterium Salmonella enterica subspecies enterica serovar Typhi or Paratyphi. Humans are the only reservoirs of S. Typhi and S. Paratyphi.

Typhoid is spread when a person drinks or eats food and water contaminated by human waste (stool or urine) containing Salmonella Typhi bacteria. The organism is often shed in the stool by chronic carriers of the bacteria. Typhoid and paratyphoid fever are not endemic in the United States. Travelers to developing countries where exposure to contaminated food or drink is likely should be vaccinated against typhoid fever before travel.

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