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Centre for International Health
Research project

Improving diagnosis of extrapulmonary TB

Alarming global tuberculosis (TB) situation makes it evident that TB control needs new tools.

Extrapulmonary tuberculosis (TB) accounts for approximately 14 to 40 % of all TB infections, and diagnosis is difficult due to paucibacillary nature of the disease. We have developed a rapid, robust, sensitive and specific immunochemistry-based assay to diagnose extrapulmonary TB by detection of the secreted mycobacterial antigen MPT64 from fluids, aspirates and biopsies.

Using Mycobacterium tuberculosis complex specific nested-PCR as gold standard the sensitivity and specificity of the assay is up to 95%, significantly better than acid-fast staining and culture (sensitivity of 12% and 22% respectively). The assay can differentiate between pathological and atypical mycobacteria and performs equally well in HIV co-infected patients. Lower costs and robustness makes it suitable for implementation in TB endemic countries.

The main objective of this project is to improve the assay by producing a functional monoclonal antibody, implementation and validation of the assay in routine diagnostic settings, and compare the assay with the WHO endorsed Xpert MTB/RIF automated molecular assay. A hospital implementing WHO endorsed DOTS strategy and a pathology laboratory will be selected from each of the 5 sites; Tanzania, Zanzibar, India, Pakistan, and Norway. All consecutive TB suspects (minimum 400 cases) will be enrolled for one year. Clinical data and samples will be collected.

The assay will be performed in addition to the routine diagnostic work-up on all samples. This cohort will be followed up from diagnosis to the completion of treatment. Response to treatment will define a TB case. Interviews, pre-designed questionnaire, and data from two comparable control hospitals from each site will be used to measure the outcomes which includes validation of the test, feasibility of implementation, increase in case detection of adults and childhood TB, and cost effectiveness analysis for future scale-up. This assay has a great potential for improving the diagnosis of extrapulmonary TB.