Widal test
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The Widal test is a serological test for Salmonella typhi.
It is a demonstration of salmonella antibodies against antigens O-somatic and H-flagellar in the blood.
It is used to ascertain the presence of typhoid fever. However, it is not a very accurate method, since we are often exposed to other bacteria (e.g. Salmonella enteritidis, Salmonella typhimurium) in this species that induce cross-reactivity; many people have antibodies against this enteric pathogens, which also react with the antigens in the Widal test, causing a false-positive result. Typhidot is the other test used to ascertain the presence of typhoid fever.
As with all serological tests, the rise in antibody levels needed to make the diagnosis takes 7-14 days, which limits their use.
Other means of diagnosing Salmonella typhi (and paratyphi) include cultures of blood, urine and feces. The organism also produces H2S from thiosulfate.
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[edit] References
- Olopoenia LA, King AL. Widal agglutination test - 100 years later: still plagued by controversy. Postgrad Med J 2000; 76(892): 80-4. PMID 10644383
