Study of Baseline Widal Titre against Salmonella Species amongst Healthy Individuals in Thiruvananthapuram District of Kerala, South India

Objective: To determine the distribution pattern of agglutinating antibodies to Salmonella enterica serotype typhi, paratyphi A and
paratyphi B antigens in normal population of Thiruvananthapuram District, Kerala, South India.
Methods: One hundred apparently healthy different age group volunteers both male and female free from infectious and other cardiac,
lung and kidney diseases were enrolled for blood collection. Sera were separated from collected blood and serially diluted in such a way
that 1:20, 1:40, 1:80, 1:160 and 1:320 by using isotonic normal saline. Widal test was performed and after incubation the test tube was
examined visually for agglutination.
Results: Among the 100 blood samples collected from healthy individuals from different areas of Trivandrum District, 64 individuals
had significant antibody titers ( 1:20) against one of the four antigens against S. enterica. In this 51 samples with an anti-O titer against
serotype typhi, 16 and 33 samples had titers of 1:60 and 1:40, respectively. A proportion (2% of all) had anti-O titer of 1:80.
Similarly, among the 59 samples demonstrating anti-H titers of 1:20 to S. enterica serotype typhi, 24 had a titer of 1:80 and 14 had
1:160. For S. enterica serotypes paratyphi A and B, anti-H titers of 1:20 were found only in 12% and 3%, respectively of all samples
tested.
Conclusion: It is found out that the cutoff value of antibody titers against Salmonella enterica typhi, paratyphi A and paratyphi B is 1:80
in case of O antigen and 1:160 in case of H antigen. From this study it is clear that the baseline titre of Salmonella antibodies in healthy
individuals in a locality should be observed at regular intervals.