Study of the Baseline Widal Titre Amongst Healthy Individuals in Amlapuram, India

Purpose: The interpretation of the Widal test depends upon the baseline titre which is prevalent amongst healthy individuals in a particular geographical area. Hence, this study was undertaken to determine the baseline Widal titre (titre of the antibodies to the O and H antigens of S. typhi and the H antigens of S. paratyphi A and B) amongst apparently healthy individuals in Amlapuram, Andhra Pradesh, India. Materials and Methods: Blood samples were collected from healthy blood donors (n=490) who attended our blood bank from September 2011 to Nov 2011. The Widal tube agglutination test was carried out. 0.4 ml of two fold serially diluted patients' sera (dilutions from 1:20 to 1:320) in 0.9% normal saline was tested by adding an equal amount of antigen. Results: Of the 490 serum samples which were tested, 270 serum samples were positive for agglutinins (1 >= in 20) and 220 serum samples were negative for agglutinins (1 >= in 20). However, 96% samples showed a titre which was equal to or less than 1 in 40 to the O antigen and 91% samples had a titre which was equal to or less than 1 in 40 to the H antigen of Salmonella enterica serovar typhi. The baseline titre for the O and H antibodies of S. typhi was found to be 1:40. The baseline titre for the Salmonella enterica serovar paratyphi A 'H' antigen was found to be =1: 40 in all the 15 samples. Conclusion: Based upon the results of our study, it has been recommended that the significant titre of the 'H' agglutinins and the 'O' agglutinins of Salmonella enterica serotype typhi was >= 1:80. While the significant titre of the 'H' agglutinins of Salmonella enterica serotype paratyphi A was >= 1: 40, the significant titre of the 'H' agglutinins of Salmonella enterica serotype paratyphi B was >= 1:20.