Significance of reduced reactivity in ELISPOT assay to RD antigens of Mycobacterium tuberculosis in BCG vaccinated individuals exposed to a patient with tuberculosis.

Children with previous BCG immunization, who were investigated for mycobacterium tuberculosis infection during an outbreak of tuberculosis, were found to have a reduced reactivity in a gamma interferon release assay for mycobacterium tuberculosis. This may represent reduced presence of mycobacterium tuberculosis in BCG vaccinated individuals, who eliminated infection due to enhancement of the immune response by immunization. Alternatively bacterial load may have been suppressed below detection threshold of the body's immune system. Future research needs to develop methods of direct and specific detection of low bacterial loads of mycobacterium tuberculosis in vivo. One method worth further development is radio-immuno-szintigraphy, which has been successful in detection of mycobacterium tuberculosis in vivo in animal studies.