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.

Use of patient-specific Leptospira isolates in the diagnosis of leptospirosis employing microscopic agglutination testing (MAT).

Given the protean manifestations of leptospirosis, adequate laboratory support for diagnosis is necessary. Traditionally, the gold standard is the microscopic agglutination test (MAT) using a panel of Leptospira isolates representing a broad range of serogroups and serovars. It has been proposed that screening with serovars circulating in a region would enhance test performance. We assessed the diagnostic usefulness of MAT using both regionally obtained clinical Leptospira isolates and the specific isolates recovered from the tested patients. Serum obtained from 41 acute febrile patients (obtained on average 7.2 days [SD±5.2] after onset of fever) was tested using a standard panel of 24 serovars along with regional isolates recovered from human and animal blood cultures from different regions in Egypt and a patient's own isolate, if available, to establish additional MAT panels. Serum samples tested by a standard 24 panel with a cut-off of >1:800 revealed five patients with positive serology. Only one patient had a positive result using a regional panel or patient's own culture developed MAT. However, the serovar with the highest titers did not match the cultured serovar. Region-specific MATs did not appear to be reliable in detection of infection or in identifying the infecting serovar.