Human Health And Disease

Typhoid fever is a bacterial disease caused by Salmonella typhi, and its confirmatory laboratory diagnosis classically relies on the Widal test, which detects rising antibody titres against the pathogen in the patient's serum. The bacterium enters the body through contaminated food and water, reaches the small intestine, and then migrates through the intestinal wall into other organs via the bloodstream, producing sustained high fever, weakness, stomach pain, and constipation. Streptococcus pneumoniae causes pneumonia, an infection of the alveoli of the lungs, and is not diagnosed by the Widal test, so it is incorrect. Haemophilus influenzae is another respiratory pathogen causing pneumonia and is unrelated to typhoid diagnosis. Wuchereria bancrofti is not even a bacterium; it is a filarial worm causing elephantiasis, making it clearly wrong. As stated in NCERT Class 12, Chapter 8 (Human Health and Disease), the historic case of Mary Mallon (Typhoid Mary) illustrated how a carrier could spread Salmonella typhi. As a sanity check, only Salmonella typhi simultaneously matches a bacterial intestinal infection and a positive Widal test, confirming it as the correct causative organism among the options provided.