Widal test

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.

Other means of diagnosing Salmonella typhi (and paratyphi) include cultures of blood, urine and feces.