Poor Performance of a Novel Serological Test for Diagnosis of Pulmonary Tuberculosis in Bangui, Central African Republic

Abstract

We assessed the performance of a serological test for tuberculosis (SDHO Laboratories Inc., Canada) in our setting. Among 68 of 99 suspected pulmonary tuberculosis patients who were scored as having tuberculosis on the basis of Mycobacterium tuberculosis-positive culture, the sensitivity of the serological test was lower than that of sputum smear microscopic examination (20.6% versus 80.9%, respectively; P < 0.000001).Tuberculosis (TB) remains a major health problem, with an estimated 8 million new cases and 2 million deaths due to this disease every year worldwide (4). Microscopic examination of sputum smears is still the only rapid, technically simple, and inexpensive test available for the routine diagnosis of TB in most developing countries. However, its sensitivity for pulmonary tuberculosis (PTB), even in good centers, is only about 60 to 70% with reference to sputum culture. Various antibodybased serological tests have been developed. Unfortunately, most do not perform sufficiently well to be used as routine field diagnostic tests (6,9,11,12). Here, we assessed the diagnostic performance of the SDHO MTB test (SDHO Laboratories Inc., Canada), a novel and commercially available serological test for the detection of PTB, in the Central African Republic, which is a setting with high prevalences of both TB (13) and human immunodeficiency virus (HIV) infection (1, 7).Study participants were recruited from the Department of Medicine at Bangui Community Hospital and from the Chest Clinic at National Teaching Hospital in Bangui, Central African Republic, between 12 July and 1 September 2004. Eligible participants were suspected PTB cases, defined as patients who had a history of cough lasting Ն3 weeks and who were identified by a physician as needing an evaluation for TB. Giving of informed consent, age of Ն18 years, and either sex were considered inclusion criteria for the study. All consecutive suspected PTB patients who fulfilled the inclusion criteria were enrolled and underwent an evaluation that is considered routine for suspected PTB in the Central African Republic. This consisted of providing three sputum specimens for acid-fast bacillus smearing within 48 h of enrollment. In addition, these same sputum specimens and blood samples were processed for mycobacterial culture (3, 5). Blood samples were also used for HIV testing as described elsewhere (8).The SDHO MTB test (SDHO Laboratories Inc., Canada) utilizes the principle of immunochromatography and is a unique two-site immunoassay on a membrane. As the test sample flows through the membrane assembly of the device, a colored recombinant TB antigen-colloidal gold conjugate complexes with anti-TB antibodies in the sample. This complex moves through the membrane to the test region, where it is immobilized by the recombinant TB antigen coating of the membrane, leading to formation of a colored band which confirms a positive test result. The absence of this colored band in the test region indicates a negative test result. The unreacted conjugate and unbound com...

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Commercial Serological Tests for the Diagnosis of Active Pulmonary and Extrapulmonary Tuberculosis: An Updated Systematic Review and Meta-Analysis

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