Exogenous reinfection as a cause of recurrent tuberculosis after curative treatment

Background For decades it has been assumed that postprimary tuberculosis is usually caused by reactivation of endogenous infection rather than by a ne w, exogenous infection. Methods We performed DNA fingerprinting with restriction-fragment-length po lymorphism analysis on pairs of isolates of Mycobacterium tuberculosis from 16 compliant patients who had a relapse of pulmonary tuberculosis after cu rative treatment of post-primary tuberculosis. The patients lived in areas of South Africa where tuberculosis is endemic. Medical records were reviewe d for clinical data. Results For 12 of the 16 patients, the restriction-fragment-length polymorp hism banding patterns for the isolates obtained after the relapse were diff erent from those for the isolates from the initial tuberculous disease. Thi s finding indicates that reinfection was the cause of the recurrence of tub erculosis after curative treatment. Two patients had reinfections with a mu ltidrug-resistant strain. All 15 patients who were tested for the human imm unodeficiency virus were seronegative. Conclusions Exogenous reinfection appears to be a major cause of postprimar y tuberculosis after a previous cure in an area with a high incidence of th is disease. This finding emphasizes the importance of achieving cures and o f preventing anyone with infectious tuberculosis from exposing others to th e disease. (N Engl J Med 1999;341:1174-9.) (C)1999, Massachusetts Medical S ociety.