The Widal test in a normal healthy population in the Sudan.

The Widal test was performed in 114 normal individuals from the Gezira area in Sudan. Salmonella typhi O agglutinins were found at a titre of 1.320 in 12 (10.5%) of them. Salmonella paratyphi A agglutinins were found at 1.160 in 5 (4.3%) and Salmonella paratyphi B "O" agglutinins were found in 6 (5.3%) at a titre of 1.160. None of these individuals had a history of typhoid fever or vaccination with TAB vaccine. The following points emerged: (i) normal healthy people in the Sudan have high antibody titres of Salmonella typhi; (ii) the Widal test in the Sudan should be interpreted against this background; (iii) previous diagnostic titre of 1.160 for S. typhi results in high false positive results; (iv) a titre above 1.320 is suggested as diagnostic for S. typhi; 1.160 for both S. partyphi B and S. paratyphi A.