Salmonella typhi bacteria cause typhoid fever, it is an acute illness related to fever. Another related bacteria salmonella paratyphi causes a less severe illness compared to the former bacteria. These bacteria are deposited in food and water through human carrier, which spreads further to other people. Typhoid fever has decreased in United States since the 1990s. The bacteria multiply in the blood stream and infect the white blood cells too. Typhoid fever can last up to four to six weeks after incubation. Symptoms of typhoid fever are poor appetite, headaches, fever, lethargy, general aches, and pains. Chest congestion and abdominal pain are common.