Typhoid fever is a bacterial infection of the intestine caused by Salmonella typhi bacteria. In the 19th century, it was a serious public health problem around the world. Today Typhoid fever is rare in industrialized countries, but remains a serious health threat in the developing world. Typhoid fever spreads through contaminated food and water or through close contact with someone who is infected. Signs and symptoms usually include high fever, headache, abdominal pain, and either constipation or diarrhea.