[Evaluation of the Widal-Felix serodiagnostic test in Togo]

To evaluate the efficacy of Widal-Felix serodiagnostic testing in Togo.

This study using a cohort of 200 patients recruited at hospitals in Lome and Atakpame from November 2005 to April 2006 was designed to compare the sensitivity and specificity of the routinely used technique (plate agglutination) and reference technique (tube agglutination).

Findings showed that the prevalence of typhoid fever was 1.5% while that of paratyphoid fever was nil. The hardest-hit age group was young people between 11 to 20 years. Men were two times more likely than women to be infected (sex-ratio, 0.5). The most useful symptoms for discriminating patients seropositive for Salmonella typhi from other serological profiles were abdominal pain (p<0.034) and diarrhea (p<0.008). The thick-drop malaria test was positive in all 3 patients (100%) with proven typhoid fever in comparison with 3.9% of the 154 patients with negative Widal-Felix serodiagnostic tests and 26.2% of the 42 patients with intermediate serological profiles. The sensitivity and specificity of the plate technique were 60.0% and 98.06% respectively. The sensitivity and specificity of laboratory analysis were 60.0% and 91.08% respectively.

The gap between the specificity of the routine plate technique and laboratory analysis underscores the difficulty of performing and interpreting the Widal-Felix serodiagnostic test. The low sensitivity and specificity of the Widal-Felix serodiagnostic test also cast doubt on systematic use for diagnosis in patients presenting fever and on initiation of antibiotic treatment based on agglutination of a single antigen. To improve the specificity of the Widal-Felix serodiagnostic test, we recommend standardization of interpretation criteria and use of tube agglutination. We also see the need for development of another reproducible immunologic test for the diagnosis of typhoid and paratyphoid infections.