Typhoid fever is an acute, life-threatening, febrile illness caused by the bacterium Salmonella subspecies enterica serotype Typhi. Because humans are the only known natural host for Salmonella Typhi, fecal-oral transmission through contaminated food and water is the most common mode of infection. In the United States, about 300 cases are reported each year, and the majority of these are acquired while traveling internationally.1,2,3
Salmonella Typhi, like other Salmonella, is a gram-negative, flagellated, non–lactose-fermenting bacillus. It is identified by its biochemical properties and somatic (O) and flagellar (H) antigens. Most freshly isolated strains have a capsular (Vi) antigen.4 In the Kauffman-White schema, Salmonella Typhi is a member of Salmonella group D, characterized by O antigens 9 and 12, and a single flagellar antigen (H). The organism survives well in water and sewage, but is readily killed by pasteurization.5
In studies of volunteers, ingesting as few as 105 bacteria has caused clinical illness in a few, and ingestion of 106 organisms results in 50% of subjects becoming ill.7 Incubation periods have been as short as 3 days and as long as 56 days; a higher inoculum is associated with shorter incubation periods. The median incubation period for a dose of 105 organisms was 9 days, for 106 organisms 7 days, and for 108 organisms 5 days.7 Partial immunity follows clinical illness, but reinfection and illness can still occur after a large oral dose. Antibody titers are not correlated with resistance to reinfection or occurrence of relapse.
Typhoid fever has an insidious onset characterized by fever, headache, constipation, malaise, chills, and myalgia.4,5 Many patients cough for the first few days of illness, and some report sore throat or joint pain. Splenomegaly, leukopenia, and abdominal distention and tenderness are generally present. Early in the illness, small, discrete, rose-colored spots caused by bacterial emboli in the skin capillaries may appear on the trunk. Diarrhea is uncommon, and vomiting is not usually severe. In children, the disease presentation is often atypical, and respiratory symptoms and diarrhea are often present.6 Complications of typhoid fever include confusion, delirium, intestinal perforation, and death. Chronic carriage of Salmonella Typhi, defined as fecal shedding of the organism for greater than one year after acute illness, occurs in 1–4% of patients.5,9
The most commonly used methods of diagnosis are blood culture and serologic assays. The sensitivity of a single blood culture has been estimated at about 50%.8 Salmonella Typhi is most frequently isolated from blood during the first week of illness, but it can also be isolated during the second and third weeks of illness, during the first week of antimicrobial therapy, and during clinical relapse. Fecal cultures are ...