In this article, we will discuss the Diagnosis of Typhoid Fever. So, let’s get started.
The diagnosis is suggested by the clinical features; whereas the definite diagnosis still depends on the isolation of the organism from culture blood or bone marrow, rose spots, stool culture, the overall yield of culture is disappointingly low about 90% in the first week, falls to less than 50% in untreated patient during third week. Yield can be approximately 100% when both blood and bone marrow culture are done in patients not receiving antibiotics. Stool culture may be positive in 75% cases during third week, while it is negative during first week. The culture of intestinal (duodenal) secretions aspirated through Riley’s tube gives better results than stool culture.
Serological diagnosis is made by Widal test which is less reliable than culture. In the absence of immunization, a higher titre of agglutinins on Widal test (1:300) is suggestive but not diagnostic. A four-fold rise in antibody titre between paired sera samples is highly suggestive. Rapid tests (typhi dot test) to detect antibodies to outer membrane proteins or antigen are available in developing countries (India) but have lower positive predictive value than culture.
DNA probe have been developed for identifying S.typhi from culture isolates and from blood. Recently a PCR based test using two pairs of oligonucleotide from a fragment of S.typhi flagellum gene (H1d) was found to be 93% sensitive and 100% specific on clinical trials, but still is not commercially available. Another test- PCR based on the nucleotides sequencing using Vi antigen Vab region has been developed. In addition there may be leukopenia or neutropenia is about 50% cases.