[Study of the Widal test phenotypic expression of blood groups ABO, Rh and MNSs in patients with typhoid fever].

The significance of the Widal test (WT) as a phenotypical expression was investigated in a cross-sectional study of 244 children from the Northern Area of Santiago (Chile) with bacteriologically confirmed typhoid fever (TF) due to S. typhi (183 cases) and S. paratyphi B (61 cases). The working hypothesis was that if the parasite-host relationships were similar for these two agents the immune response, as measured by the Widal test, should be similar. An association between test response and etiology was found consisting of a significantly higher proportion of positive response, in cases due to S. paratyphi B as compared with those due to S. typhi, (OR = 2.13; 95 Cl% = 1.06, 4.32; p = 0.02). Stratified analysis showed that although the association between etiologic agent and Widal test response persisted within all strata, significant interactions could be shown as evidenced by the magnitude of the associations, which varied according to blood phenotypes as well as gender (Mantel-Haenszel test for heterogeneity for 0, p < 0.034; for RH5 p < 0.033; for SS, ss p < 0.056; and gender p < 0.033). These results support the hypothesis that the Widal test response is a phenotypical marker eventually useful for studying human genetic heterogeneity in typhoid fever. The implications of these findings regarding previous study results and the possible role of S. paratyphi B in typhoid fever and its related conditions are discussed.