Recurrence of tuberculosis in a low-incidence setting.

Recurrence of active tuberculosis following treatment of an initial disease episode can occur due to endogenous re-activation or exogenous re-infection. Cases of recurrent tuberculosis in the Australian state of New South Wales between 1994 and 2006 were identified by data linkage analysis with confirmatory review of case notes. Patients with more than one culture-positive disease episode during that time period who had completed treatment for the initial disease episode were included. Genotyping of Mycobacterium tuberculosis was used to determine whether recurrence was likely to be due to re-activation or re-infection. There were 5,723 tuberculosis notifications between 1994 and 2006, 3,731 of which were culture-positive. Fifteen (0.4%) patients had recurrent culture-positive disease over a mean 5.7 yrs of follow-up (crude annual incidence 71 per 100,000 population). Recurrent tuberculosis was attributable to re-activation (indistinguishable strains) in 11 (73%) cases and to re-infection (different strains) in four (27%). In a low-incidence setting of tuberculosis, a control programme incorporating directly observed therapy for active disease resulted in a very low rate of recurrent tuberculosis over a long period of follow-up. Re-infection is less likely than re-activation, but still contributes significantly to the number of cases with recurrent disease.