Distribution of antibody titer against Salmonella enterica among healthy individuals in nepal.

BACKGROUND

Enteric fever is an endemic problem in Nepal and Widal agglutination test is widely used for its diagnosis but a normal baseline titer in healthy population and cutoff values have not been established.

METHODS

We measured average baseline antibody titers against "O" and "H" antigens of Salmonella enterica serotype Typhi and "H" antigens of serotypes Paratyphi A and Paratyphi B among apparently healthy blood donors in Nepal. The antibody titers were measured using Standard Widal Confirmatory Quantitative Tube test.

RESULTS

Among the 100 blood samples collected from healthy volunteers, 62 individuals had significant antibody titers (> or = 1:20) against one of the four antigens against S. enterica. Among 54 samples with an anti-O titer against serotype Typhi, 15 and 36 samples had titers of > or = 1:60 and > or = 1:40, respectively. A significant proportion (12% of all) had anti-O titer of > or = 1:80. Similarly, among the 59 samples demonstrating anti-H titers of > or = 1:20 to S. enterica serotype Typhi, 29 had a titer of > or = 1:80 and 12 had 1:160. For S. enterica serotypes Paratyphi A and B, anti-H titers of > or = 1:20 were found only in 12% and 3%, respectively, of all samples tested.

CONCLUSION

When a single Widal agglutination titer is used for the diagnosis of enteric fever, it will be more appropriate to change the currently used cutoff levels against S. enterica serotype Typhi to > 1:80 for anti-O and > 1:160 for anti-H titers for Nepal.