The “Baseline Widal Titre” Amongst Apparently Healthy Adults Working at a Tertiary Care Medical Institution, a Pilot Study, Uttarakhand, India

Introduction: As typhoid fever is known for its endemicity all over the India, healthy people may contain antibodies against salmonella typhi and paratyphi. These antibodies may react up-to a variable titre either due to past exposure, vaccination or/and cross -reacting antigen. Therefore, antibody titre in widal test varies widely from place to place and is referred as baseline titre of that particular area. Two properly staged tests (2-4 weeks interval) show about a four -fold rise in antibody levels leads to a reliable widal test. Single widal test values are not considered significant for diagnosis but many places still use this as diagnostic marker which further depends upon baseline titre prevalent in that particular area. Aims: This study was undertaken in jhajra, Uttarakhand to determine the baseline titre in this geographical region for calculating significant widal titres. Material and Methods: Blood samples were collected from apparently healthy individuals which included medical students, nursing staff, doctors, and other health care workers (aged 19-45) with proper consent. All the samples after being screened by slide agglutination test were further confirmed by Quantitative tube agglutination test, to find out the baseline titre. The tube agglutination test was carried out by taking 0.5 ml of two-fold serially diluted sera (dilutions from 1:20 to 1:320) in 0.9% normal saline with an equal amount of antigen. Results: Out of total 110 serum samples,36 (32.7%) sera were positive (titre ≥ 1:20) and 74 (67.3%) were negative(titre<1:20). A total of 36 samples were positive for agglutinins of “O” antigen,32 for agglutinins of “H” antigen,16 for paratyphi A and 10 for paratyphi B. 23 out of 36 (63.8 %) sera were positive for agglutinins of 'O' antigen of Salmonella typhi (TO) at a titre of 1:40 followed by 6 sera positive at 1:20 (16.6%) and 1:80 (16.6%) and 1 serum sample positive at 1:160 (2.77%) 59.3 % (19) sera were positive for 'H' antigen of Salmonella typhi (TH) at a titre of 1:80 and 10 % sera (11) were positive for 'H' antigen at a titre of 1:40 and 2(1.8%) were positive at 1:20.16(44.4%) sera samples were positive for of Salmonella paratyphi A (AH) and Salmonella paratyphi B (BH) respectively, both at a titre of 1:20 and 8.3% sera were positive at 1:40 respectively. Conclusion: The most frequently recorded titre of the reactive sera was 1:40 and 1:80 for anti-O antibodies and anti-H antibodies and 1:20 for AH and BH. Thus, the significant cut-off level for TO and TH was ≥ 1:80 and ≥ 1:160 that for AH and BH was ≥ 1:40.