Rapid, early and specific diagnosis of tuberculosis and other mycobacterial diseases in Burundi

The potential usefulness of ELISA based serological tests to assist in rapid, early and specific diagnosis of tuberculosis was investigated. The materials were selected, based on published data and on our preliminary findings. Initially screening tests were performed using crude antigens such as Purified Protein Derivate (PPD) and a BCG-filtrate. Unfortunately, the results with these antigens were not promising. The specificity of both antigens using sera from 94 healthy controls was 64%. As a consequence of these findings, the crude antigens were excluded from further tests, and the study was continued with purified antigens. The work focused on 2 purified proteins: Antigen 60 (A60), a lipopolysaccharide-protein complex, and P32, a stress protein produced in zinc deprived cultures, identified as Antigen 85 A in the BCG reference system, both isolated from Mycobacterium bovis BCG. The commercial A60 based ELISA and our own P32 based ELISA were used to test a total of 300 sera from HIV positive, negative and unscreened individuals, mainly originating from Burundi. These sera were collected from clinical established cases of pulmonary TB, extrapulmonary TB, and patients with non-tuberculous tropical diseases such as salmonellosis, trypanosomiasis, malaria, etc. and healthy individuals. The A60 based ELISA had a sensitivity of 76.8% for the proven cases of active pulmonary tuberculosis and 61.9% for the extrapulmonary tuberculosis cases. No difference was shown between HIV positive and HIV negative patients. Specificity reached 95.2% for healthy individuals, but dropped to 68.1% when persons with active non-tuberculous tropical diseases were included. Eighty-six percent of the pulmonary cases and 87.7% of the extrapulmonary cases were detected by the ELISA-P32. These findings suggest that this test might be useful as a confirmatory test for the diagnosis of extrapulmonary tuberculosis. Again no difference was noticed between HIV negative and positive patients. The main contraindication for the use of the ELISA-P32 for the diagnosis of tuberculosis is its low specificity: 70.2% with sera from healthy controls and 22.2% for hospitalised patients and persons with non-tuberculous tropical diseases. In a small recent prospective study 4 out of 10 HIV+ persons with no evidence for TB yielded a positive result for the ELISA-P32. Two of them developed pulmonary tuberculosis within 6 months, whereas 2 P32-positives and 6 P32-negatives remained up to now without any manifestations of tuberculosis. The difference was not significant, but the number of cases was limited.(ABSTRACT TRUNCATED AT 400 WORDS)

Publication year:1993

Keywords:Bacterial diseases, Tuberculosis, Diagnosis, Laboratory medicine, ELISA, Burundi, Africa-Central