Evaluation of a newly developed ELISA against Widal, TUBEX-TF and Typhidot for typhoid fever surveillance.

Introduction: Typhoid fever is endemic in many parts of the world and represents a major cause of acute febrile illness (AFI). Rapid and accurate laboratory methods for diagnosis of this disease are needed for both patient care and surveillance situations. Methodology: Serum samples were collected from AFI patients and used to evaluate the performance of a newly developed ELISA assay that uses a mixture of somatic and flagellar antigens to detect the total antibody response against Salmonella enterica subspecies enterica serovar Typhi ( S . Typhi) infection. The levels of Ig isotype response (IgG, IgM and IgA) were also evaluated, and results were compared to those of TUBEX-TF and Typhidot commercial kits.  Results: Of 234 culture-confirmed typhoid patients, the total Ig ELISA diagnosed 93% compared to 71% using Widal test. This sensitivity level (93%) is higher than that observed for the individual Ig ELISAs (IgG 75%; IgM 79%; IgA 57%) and the commercial tests TUBEX-TF (75%), Typhidot IgM (63%) and Typhidot IgG (28%). An agreement of 78% was achieved between the total Ig ELISA and Widal test. The average specificity of the ELISA was 96%. Using ELISA, up to 200 samples can be tested per run with cost per test at US$0.20. Conclusions: The developed ELISA shows superior sensitivity and specificity, when compared to Widal, TUBEX-TF and Typhidot assays, is more cost effective and allows higher throughput. This method is highly recommended for active surveillance studies or outbreak investigations of typhoid fever.