Widal test is carried out to test

Widal test is one of the most over utilized diagnostic tests for typhoid fever in developing countries ever since its introduction over 100 years ago. This test demonstrates the presence of somatic $(O)$ and flagellar $(\mathrm{H})$ agglutinins to Salmonella typhi in the patients serum using suspensions of $\mathrm{O}$ and $\mathrm{H}$ antigens. Antigens of S. paratyphi A and S. paratyphi B are included in most commercial kits.