Field evaluation of enzyme-linked immunosorbent assay for the serodiagnosis of tuberculosis.

An enzyme-linked immunosorbent assay (ELISA) was evaluated as a serodiagnostic test for active tuberculosis in La Paz, Bolivia. ELISA was compared with sputum smear in 277 persons presenting to the Instituto de Torax and was used for screening in 1,458 military personnel. The test was performed under field conditions on 4-microliter samples of capillary blood obtained by finger prick. ELISA was found to have a sensitivity of 69% and a specificity of 88%. Sputum smear had a sensitivity of 79% and a specificity of 100%. ELISA was found to have undiminished sensitivity and specificity in patients who were sputum-negative, and the two tests could be combined to achieve a sensitivity of 92% and specificity of 88%. Positive and negative predictive values were highest for populations with tuberculosis prevalences in the range of that seen among patients presenting to the Instituto de Torax in Bolivia, but ELISA also led to the diagnosis of tuberculosis in 5 of 1,458 soldiers tested in the screening program.

The tuberculin specificity in humans of Mycobacterium tuberculosis antigen 5.

Mycobacterium tuberculosis antigen 5 is a protein antigen limited in distribution to M. tuberculosis and M. bovis and capable of eliciting typical delayed tuberculin skin test reactions in humans. A single large batch of this antigen was purified by immunoabsorbent affinity chromatography and used to skin test patients with tuberculosis and other mycobacterial infections and healthy persons in general populations in geographic areas where nonspecific tuberculin reactivity is frequently encountered. Antigen 5 was found to be no more specific as a tuberculin antigen than PPD. If the available data are accepted, then either a disparity in antigen recognition by antibody and T lymphocytes may exist or the widely accepted hypothesis attributing nonspecific tuberculin reactivity to antigenic cross reactivity with other mycobacteria may be incorrect.