If blood sample is collected from a patient for Widal test, positive result of…

Concept

The Widal test is a serological agglutination test. It detects antibodies in a patient's blood serum that react against the O and H antigens of Salmonella enterica serotypes Typhi and Paratyphi. A significant or rising antibody titer indicates the immune system has been exposed to, or is currently fighting, an infection caused by these specific bacteria; because titers can also reflect past exposure or vaccination, blood culture remains the gold-standard confirmatory test, but the Widal reaction is the standard serological indicator used at this level.

Application

In this item, a blood sample is tested by the Widal method and returns a positive result. Since the Widal test specifically measures the agglutination reaction against Salmonella Typhi/Paratyphi antigens, a positive titer indicates enteric fever caused by these bacteria — Typhoid fever (caused by S. Typhi) being the standard interpretation used in this context among the diseases offered.

Cross-check

Checking against how the other listed diseases are actually confirmed shows each is diagnosed through an entirely different test, unrelated to the Salmonella O/H antigens that the Widal reaction targets:

• Tuberculosis is caused by the bacterium Mycobacterium tuberculosis and is investigated using sputum smear microscopy or CBNAAT/GeneXpert for active disease; the tuberculin skin (Mantoux) test indicates prior exposure/immune sensitization rather than active infection — none of these involve Salmonella antigens.

• Elephantiasis (lymphatic filariasis) is caused by filarial nematodes and is confirmed by finding microfilariae in a night blood smear, not by a Salmonella antibody reaction.

• Ascariasis is caused by the roundworm Ascaris lumbricoides and is confirmed by finding the parasite's characteristic eggs on stool microscopy, again unrelated to Salmonella antigens.

Because it specifically targets the O and H antigens of Salmonella Typhi/Paratyphi, the Widal agglutination reaction is most closely associated with these bacteria among the diseases listed here, making Typhoid the standard indicator and best-supported answer among the options offered.