Paratyphoid fever laboratory tests

Overview
A single blood culture is positive in only half the cases. Stool culture is not usually positive during the acute phase of the disease. Bone marrow culture increases the diagnostic yield to about 80% of cases. The Widal test is an old serologic assay for detecting IgM and IgG to the O and H antigens of salmonella. The test is unreliable but is widely used in developing countries because of its low cost. Newer serologic assays are somewhat more sensitive and specific than the Widal test but are infrequently available. Because there is no definitive serologic test for typhoid or paratyphoid fever, the diagnosis often has to be made clinically.

The combination of a history of risk for infection and a gradual onset of fever that increases in severity over several days should raise suspicion of typhoid or paratyphoid fever.