Pathogenesis of tuberculosis: clinical and epidemiologic perspective.

Mycobacterium tuberculosis is one of several pathogens that confer resistance to reinfection, but its persistence presents a constant threat to the host. In countries where the incidence of tuberculosis is low, most cases appear to be caused by recrudescence of old infection. The ability of the organism to produce protection against a new infection, at least in theory, affords an opportunity to induce resistance by vaccination. Although exogenous reinfection is documented in a recent paper, data from a recent outbreak of tuberculosis in Arkansas show no evidence of reinfection in the face of documented serious spread of infection to persons who were not reactive to tuberculin. Presently available vaccines have not proven to be reliable in producing resistance. Thus, a search for a means of conferring the ability to mount a quick immune response when the organism is encountered appears to be worthwhile.