ENZYME-LINKED-IMMUNOSORBENT-ASSAY (ELISA) WITH MYCOBACTERIAL CRUDE ANTIGENS FOR THE SEROEPIDEMIOLOGIC DIAGNOSIS OF ACTIVE TUBERCULOSIS

In search for reliable, nonexpensive procedures for tuberculosis diagn osis suitable for seroepidemiological studies in leprosy-endemic areas , enzyme-linked immunosorbent assays (ELISAs) with whole intact bacill i, whole lipid-free bacilli and protein-enriched soluble extracts from the H37Rv Mycobacterium tuberculosis strain were evaluated. Sera test ed came from 47 active, pulmonary tuberculosis adult cases, 60 househo ld contacts of active tuberculosis cases, 20 lepromatous leprosy adult patients, and 67 healthy adult controls obtained from low and high le prosy and tuberculosis endemicity areas. There was no influence of suc h endemicity levels in the number of positive results in control sera. Antibody levels obtained with each of the antigens in ELISAs were sig nificantly different in tuberculosis patients and the control groups. Ten percent of tuberculosis contacts were positive with some of the an tigens and three of them showed suggestive chest radiographs, The best combination for a high number of positive results with tuberculosis s era and low positive results with leprosy sera was the BCG soluble ext ract (91% and 15%, respectively). This preparation also yielded excell ent 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 pur ified antigens. In pulmonary cases, sputum microscopic examination and culture have higher sensibility than serodiagnosis; therefore, the ut ilization of BCG soluble extract ELISAs as a diagnostic aid in individ ual patients with suspected active tuberculosis only can be useful in extrapulmonary cases.