fever is still very high and oscillates very little over 24 hours. Dehydration ensues along with malnutrition, and the patient is delirious. A third of affected people develop a macular rash on the trunk. Intestinal haemorrhage due to bleeding in congested Peyer's patches occurs; this can be very serious, but is usually not fatal. Intestinal perforation in the distal ileum is a very serious complication and often fatal. It may occur without alarming symptoms until septicaemia or diffuse peritonitis sets in. Respiratory diseases such as pneumonia and acute bronchitis Encephalitis Neuropsychiatric symptoms (described as "muttering delirium" or "coma vigil"), with picking at bedclothes or imaginary objects. Metastatic abscesses, cholecystitis, endocarditis, and osteitis. Low platelet count (thrombocytopenia) is sometimes seen. Causes Bacteria The Gram-negative bacterium that causes typhoid fever is Salmonella enterica subsp. enterica serovar Typhi. Based on MLST subtyping scheme, the two main sequence types of the S. Typhi are ST1 and ST2, which are widespread globally. Global phylogeographical analysis showed dominance of a haplotype 58 (H58), which probably originated in India during the late 1980s and is now spreading through the world with multi-drug resistance. A more detailed genotyping scheme was reported in 2016 and is now being used widely. This scheme reclassified the nomenclature of H58 to genotype 4.3.1. Transmission Unlike other strains of Salmonella, no animal carriers of typhoid are known. Humans are the only known carriers of the bacterium. S. enterica subsp. enterica serovar Typhi is spread by the fecal-oral route from people who are infected and from asymptomatic carriers of the bacterium. An asymptomatic human carrier is someone who is still excreting typhoid bacteria in stool a year after the acute stage of the infection. Diagnosis Diagnosis is made by any blood, bone marrow, or stool cultures and with the Widal test (demonstration of antibodies against Salmonella antigens O-somatic and H-flagellar). In epidemics and less wealthy countries, after excluding malaria, dysentery, or pneumonia, a therapeutic trial time with chloramphenicol is generally undertaken while awaiting the results of the Widal test and blood and stool cultures. Widal test The Widal test is used to identify specific antibodies in the serum of people with typhoid by using antigen-antibody interactions. In this test, the serum is mixed with a dead bacterial suspension of salmonella with specific antigens. If the patient's serum contains antibodies against those antigens, they get attached to them, forming clumps. If clumping does not occur,