Humans are the only natural reservoirs of S. typhi. Ingestion of food or water contaminated with human faeces is the most common mode of transmission. The salmonella organisms after ingestion attack the intestine and enter into the blood stream. These organisms then the bone-marrow, liver, spleen and other organs. The bacteria again enter the blood from these organs and again reach the intestine through the bile by local multiplication in the walls of gall bladder. Circulating endotoxin (a part of the bacterial cell wall) is thought to be the cause of prolonged fever and toxic symptoms.
Some patients may excrete S. typhi for three months or longer after infection leading to a chronic carrier state.
Clinical features
Onset: Gradual onset fever, anorexia, malaise, diarrhea in early stages and then constipation.
2nd week: High fever, toxic child, delirium, enlarged liver and spleen, diffuse abdominal tenderness. A rash may be seen around 7th to 10th day on the chest and the abdomen. The fever usually resolves within 2-4 weeks but malaise and lethargy persist for a longer time.

1. Severe intestinal hemorrhage and intestinal perforation - seen usually in 1st week of illness.
2. Heart involvement in the form of shock and psychosis may also be seen.
3. Rare complications - Hepatitis (inflammation of liver), Cholecystitis (inflammation of gall bladder), pancreatitis (inflammation of pancreas), pneumonia, bone marrow involvement, pyelonephritis (inflammation of kidneys), meningitis.

Blood tests in the from of Widal test and culture may help in the diagnosis. In some patients' urine, stool and bone marrow culture may also be positive.

Your doctor will prescribe antibiotics for 7-10 days. In patients with high fever, intravenous antibiotics may be required. In children with malnutrition, antibiotic therapy can be extended for 21 days to reduce the rate of complications.
In patients with shock, obtundation, stupor or coma a short course of steroids improves the survival.
To eradicate chronic carrier stage: High dose antibiotics for 4-6 weeks are required.

1. Oral Ty21a strain S.typhi - A live attenuated preparation. Recommended in children more than 6 years of age. Four enteric coated capsules on alternate days are given.

2. Vi Capsular polysaccharide vaccine - It is given intramuscular in children less than 2 yrs of age.
Booster is required every 3 yrs.