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

Other means of diagnosing Salmonella typhi (and paratyphi) include cultures of blood, urine and feces. The organism also produces H₂S from thiosulfate.

Eponymous medical tests | Immunology | Infectious diseases

Widal