Abstract
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. 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. 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. 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.
Highlights
Typhoid fever is endemic in many parts of the world and represents a major cause of acute febrile illness (AFI)
Using sera from culture-positive patients, the newly developed total Ig ELISA showed improved sensitivity (93%, Table 1a) compared to that of the Widal test (71%, Table 1b) or previously published ELISAs [5,18,20]. Among these culturepositive samples, the total Ig ELISA detected 75% (50/67, Table 1b) of those not detected by the Widal test, while the Widal test detected only 1% (1/67, Table 1b) of culture positive samples testing negative for the total Ig ELISA
Within the probable typhoid patient samples, the total Ig ELISA detected 78% (Table 1a and 1b). This sensitivity level, lower than that observed for cultureconfirmed typhoid samples, is still comparable to or higher than those previously reported for the Widal-Table 1b
Summary
Typhoid fever is endemic in many parts of the world and represents a major cause of acute febrile illness (AFI). 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%). 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. This range is among the highest reported incidence ranges in northern African countries (10100 per 100,000 per year) [4]
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