Ans. B: Blood culture Salmonella is a Gram-negative, non spore forming, facultative anaerobic sho bacillus that is motile due to its peritrichous flagella. The bacterium grows best at 37degC (human body temperature). Typhoid fever is characterized by a sustained fever as high as 40degC (104degF), profuse sweating, gastroenteritis, and nonbloody diarrhea. Less commonly a rash of flat, rose-colored spots may appear. In the first week, there is a slowly rising temperature with relative bradycardia. There is leukopenia with eosinopenia and relative lymphocytosis, a positive diazo reaction and blood cultures are positive for Salmonella Typhi or Paratyphi. The classic Widal test is negative in the first week. In the second week of the infection, the patient lies prostrated with high fever in plateau around 104degF (40degC) and bradycardia (Sphygmo-thermic dissociation), classically with a dicrotic pulse wave. Delirium is frequent. This delirium gives to typhoid the nickname of "nervous fever". Rose spots appear on the lower chest and abdomen in around 1/3 patients. There are rhonchi in lung bases. Diarrhea can occur in this stage: green with a characteristic smell, comparable to pea-soup. The spleen and liver are enlarged (hepatosplenomegaly). The Widal reaction is strongly positive with anti 0 and anti H antibodies. Blood cultures are sometimes still positive at this stage. In the third week of typhoid fever a number of complications can occur: Intestinal hemorrhage due to bleeding in congested Peyer's patches; this can be very serious but is usually non-fatal. Intestinal perforation in distal ileum: this is a very serious complication and is frequently fatal. Encephalitis Metastatic abscesses, cholecystitis, endocarditis and osteitis The yield of blood cultures is variable; sensitivity is as high as 90% during the first week of infection and decreases to 50% by the third week.