<P> In 1896 and named after its inventor, Georges - Fernand Widal, is a presumptive serological test for enteric fever or undulant fever whereby bacteria causing typhoid and malaria fever are mixed with a serum containing specific antibodies obtained from an infected individual . In cases of Salmonella infection, it is a demonstration of the presence of O - soma false - positive result . Test results need to be interpreted carefully to account for any history of c fever, typhoid vaccination, and the general level of antibodies in the populations in endemic areas of the world . Typhidot is the other test used to ascertain the diagnosis of typhoid fever . As with all serological tests, the rise in antibody levels needed to perform the diagnosis takes 7--14 days, which limits its applicability in early diagnosis . Other means of diagnosing Salmonella typhi (and paratyphi) include cultures of blood, urine and faeces . These organisms produce H S from thiosulfate and can be identified easily on differential media such as bismuth sulfite agar . </P> <P> 2 - mercaptoethanol is often added to the Widal test . This agent more easily denatures the IgM class of antibodies, so if a decrease in the titer is seen after using this agent, it means that the contribution of IgM has been removed leaving the IgG component . This differentiation of antibody classes is important as it allows for the distinction of a recent (IgM) from an old infection (IgG). </P> <P> The Widal test is positive if TO antigen titer is more than 1: 160 in an active infection, or if TH antigen titer is more than 1: 160 in past infection or in immunized persons . A single Widal test is of little clinical relevance due to the high number of cross-reacting infections, including malaria . If no other tests (either bacteriologic culture or more specific serology) are available, a fourfold increase in the titer (e.g., from 1: 40 to 1: 640) in the course of the infection, or a conversion from an IgM reaction to an IgG reaction of at least the same titer, would be consistent with a typhoid infection . </P> <P> A new serological test called the Tubex test is neither superior nor better performing than the Widal test . Therefore, Tubex test is not recommended for diagnosis of typhoid fever . </P>

What does it mean if widal test is positive
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