Typhoid fever is characterized by severe systemic illness with fever and abdominal pain . The organism classically responsible for the enteric fever syndrome is S. enterica serotype Typhi (formerly S. typhi). Other Salmonella serotypes, particularly S. enterica serotype paratyphi A, B, or C, can cause a similar syndrome; however, it is usually not clinically useful or possible to reliably predict the causative organism based on clinical findings . The term "enteric fever" is a collective term that refers to both typhoid and paratyphoid fever.
The epidemiology, microbiology, clinical manifestations, and diagnosis of typhoid fever will be reviewed here. The pathogenesis, treatment and prevention of typhoid fever are discussed separately. (See "Pathogenesis of typhoid fever" and "Treatment and prevention of typhoid fever" and "Immunizations for travel".)
Typhoid fever is more common in children and young adults than in older patients . Worldwide, typhoid fever is most prevalent in impoverished areas that are overcrowded with poor access to sanitation. Non-epidemic incidence estimates suggest that south-central Asia, Southeast Asia, and southern Africa are regions with high incidence of S. typhi infection (more than 100 cases per 100,000 person years) . Other regions of Asia and Africa, Latin America, the Caribbean, and Oceania have a medium incidence of 10 to 100 cases per 100,000 person years. These estimates, though, are limited by lack of consistent reporting from all areas of the world and are based on extrapolation of data across regions and age groups. As an example, the incidence estimates within Africa are based upon reports from Egypt and South Africa only and thus may not be accurately defined.
Because humans are the only reservoir for S. enterica serotype Typhi, a history of travel to settings in which sanitation is poor or contact with a known typhoid case or carrier is useful for identifying people at risk of infection outside of endemic areas, although a specific source or contact is identified in a minority of cases.
Approximately 200 to 300 cases of S. typhi are reported in the United States each year . About 80 percent of these cases occur among travelers to countries where typhoid fever is endemic, particularly countries in South-Central Asia. In a study of 428 cases of typhoid fever reported among travelers from resource rich countries through the multinational GeoSentinel Surveillance Network between 2006 and 2011, 67 percent of cases were acquired in south-central Asia (34, 13, 7, and 6 percent of total from India, Nepal, Pakistan, and Bangladesh, respectively) (figure 1) . Individuals visiting relatives in endemic countries accounted for 28 percent of the typhoid cases.