National Advisory Committee on Immunization (NACI). Supplementary statement on Typhim VI polysaccharide capsular vaccine.

Typhoid fever is caused by Salmonella typhi, which differs from most other Salmonella species in that it infects only humans and frequently causes severe systemic illness. It is usually transmitted by food and drink that has been contaminated with fecal material from a patient with typhoid fever or an asymptomatic carrier of S. typhi. The fatality rate ranges from 16% in untreated cases to less than 1% in those given appropriate antibiotic therapy. Chronic carriage, which may last for years, develops in 2% to 5% of cases. The risk of severe illness is increased in persons with diminished gastric acid levels due to gastrectomy or treatment with antacid or H2-antagonists, or in immunocompromised persons, e.g., AIDS patients and chemotherapy recipients.