Ghazala Jaffery, Muhammad Saeed Anwar, Waqar Hussain, Sajid Maqbool.
Serological diagnosis of typhoid fever in children: a comparative evaluation of Salmonella Typhi O-9 antigen based rapid assay.
Pak Paed J Jan ;29(1):27-33.

Objective: To evaluate the Salmonella typhi O-9 antigen based rapid assay (TUBEX) for serological diagnosis of typhoid fever in children. Design: A prospective, cross sectional, descriptive study. Place and duration of study: The study was conducted between January 2003 and June 2004 at the Department of Immunology, The Children`s Hospital & lnstitute of Child Health, Lahore and Department of Paediatrics, Shaikh Zayed Hospital, Lahore. Subjects and methods: A total of 103 children with clinically suspected typhoid fever, from Children`s Hospital & Institute of Child Health, Lahore and Shaikh Zayed Hospital, Lahore were included in the study. Twenty-six children with other febrile illnesses were included as controls. Both male and female patients, upto17 years of age were investigated. All the patients were subjected to blood culture test for isolation of Salmonella typhi using standard microbiology techniques. At the same time sera of these patients were tested for anti-Salmonella typhi antibodies using TUBEX, Typhidot and Widal tests for the serological diagnosis of Salmonella typhi infection. Results: Out of 103 patients with suspected typhoid fever, 28 (27.18%) patients had blood culture-proven typhoid, while 75 (72.82%) cases had negative blood culture and thus had clinical-typhoid. None of the patients with non-typhoid illness had blood culture positive for Salmonella typhi (S.typhi). In the entire cohort of 103 cases (clinical and culture proven typhoid) n=103, TUBEX test was positive in 89 (86.41%), Typhidot test in 77 (74.76%) and Widal test in 72 (69.90%) patients respectively. In the non-typhoid group TUBEX test was positive in 4(15.38%), Typhidot in one (3.85%) and Widal test in 7(26.92%) patients respectively. Comparative evaluation of the serological tests in the entire cohort (n=103) showed that the sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of TUBEX Test were 86.41%, 84.62%, 95.70% and 61.11% respectively. Typhidot test had sensitivity of 74.76%, specificity of 96.15%, PPV of 98.72% and NPV of 49.02%. Widal test had sensitivity of 69.90%, specificity 73.08%, PPV 91.14% and NPV 38.00%. Evaluation of the serological tests in the culture-proven typhoid fever group revealed that TUBEX test had sensitivity of 89.29% specificity of 84.62%, PPV 86.21% and NPV 88.00%. Typhidot had sensitivity of 82.14%, specificity 96.15%, PPV 95.83% and NPV 83.33% while Widal test had sensitivity, specificity, PPV and NPV of 64.29%, 73.08%, 72.0% and 65.52% respectively. Conclusion: TUBEX test is more sensitive as compared to typhidot test. However its specificity is slightly lower. It is a useful rapid test for serological diagnosis of typhoid fever in children.

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