Enzyme-linked immunosorbent assay (ELISA) with mycobacterial crude antigens for the sero-epidemiological diagnosis of active tuberculosis.

In search for reliable, nonexpensive procedures for tuberculosis diagnosis suitable for seroepidemiological studies in leprosy-endemic areas, enzyme-linked immunosorbent assays (ELISAs) with whole intact bacilli, whole lipid-free bacilli and protein-enriched soluble extracts from the H37Rv Mycobacterium tuberculosis strain were evaluated. Sera tested came from 47 active, pulmonary tuberculosis adult cases, 60 household contacts of active tuberculosis cases, 20 lepromatous leprosy adult patients, and 67 healthy adult controls obtained from low and high leprosy and tuberculosis endemicity areas. There was no influence of such endemicity levels in the number of positive results in control sera. Antibody levels obtained with each of the antigens in ELISAs were significantly different in tuberculosis patients and the control groups. Ten percent of tuberculosis contacts were positive with some of the antigens and three of them showed suggestive chest radiographs. The best combination for a high number of positive results with tuberculosis sera and low positive results with leprosy sera was the BCG soluble extract (91% and 15%, respectively). This preparation also yielded excellent sensitivity and specificity values for tuberculosis (91.5% and 92.5%, respectively). These data suggest that BCG soluble extract ELISAs could provide helpful information to estimate tuberculosis prevalence only in leprosy-free areas, under a situation of unavailability of purified antigens. In pulmonary cases, sputum microscopic examination and culture have higher sensibility than serodiagnosis; therefore, the utilization of BCG soluble extract ELISAs as a diagnostic aid in individual patients with suspected active tuberculosis only can be useful in extrapulmonary cases.