Rapid Direct Antigen Test for Tuberculosis

Coordinator:  C. Boehme PhD

Lab Coordinator: M. Gerhardt PhD

Lab Coordinator: S. Dufke

The main purpose of the proposed project is the development and clinical evaluation of a rapid direct antigen test for diagnosis of pulmonary tuberculosis using an immunochromatographic test format. One major obstacle in the fight against tuberculosis is the lack of an inexpensive, easy to use and sensitive method to detect TB infected patients. The only method that is affordable in many parts of the developing world is the microscopy smear test. It is used to detect TB-patients and monitor their treatment success. Unfortunately this test is labour intensive and is mainly used to detect “productive, open”, pulmonary TB. In addition, the sensitivity depends dramatically on the quality of the test performers. More advanced methodologies such as culture and PCR are technically difficult, not that reliable and therefore not widespread in rural Africa.

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Together with a company that developed a prototype rapid direct antigen immunoassay detecting the presence of Mycobacterium tuberculosis in clinical specimens such as urine, blood and sputum, we want to explore the sensitivity and specificity in an African clinical setting. Immunological assays detecting directly TB antigens or antibodies against TB have been identified as most promising candidates to substitute and complement smear testing.
In a first clinical evaluation the LAM assay has proven to have a high sensitivity and specificity in 231 patients with suspected pulmonary tuberculosis (TB) and 103 healthy volunteers were screened with standard TB tests and with the new LAM-ELISA. Of 132 patients with confirmed pulmonary mycobacterial disease (positive sputum culture), 106 were positive using the LAM-ELISA (sensitivity 80.3%). In comparison, the sensitivity of acid-fast bacilli (AFB) sputum microscopy was 62.1% (82 of 132 confirmed cases).
Of the 231 patients, 17 were both culture- and AFB-negative, but had typical radiographic signs of pulmonary mycobacterial infection and did not respond to antibiotic treatment. Of these17 patients, 13 (76.5%) had positive LAM-ELISA test results. To define the specificity of the assay, urine samples from 103 healthy volunteers were also screened using LAM-ELISA. All but one had an optical density below the cut-off (specificity 99%).
Of interest was a significant correlation between the level of microscopic density of mycobacteria in sputum and LAM antigen concentration in urine (χ2=8.44). The LAM-ELISA is a field-adapted tool that can improve screening standards in countries with a high incidence of TB.
We are currently conducting a much larger final phase III evaluation in TB suspect patients in Mbeya.

This research is jointly funded by Chemogen Inc., Portland, USA, FIND (Foundation for new innovative diagnostics), Geneva, CH and University of Munich, Germany

Partners involved in the project are the Mbeya Regional TB & Leprosy Program, the Dept. of Infectious Diseases and Tropical Medicine at the LMU, Munich and Chemogen Inc, Portland, ME, USA, FIND, Geneva, CH

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