Exogenous reinfection as a cause of multidrug-resistant and extensively drug-resistant tuberculosis in rural South Africa.

BACKGROUND Multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) are now major threats in areas of South Africa with a high prevalence of TB and human immunodeficiency virus (HIV) infection. The role of exogenous reinfection as a cause of MDR and XDR TB in these settings has not been determined. METHODS We reviewed data from patients with culture-positive TB who later developed MDR or XDR TB in Tugela Ferry, KwaZulu-Natal, South Africa during 2005-2006. We performed spoligotyping on initial isolates (obtained at the time of treatment initiation) and follow-up isolates obtained from these patients. RESULTS We identified 23 patients who developed MDR or XDR TB after being treated for less resistant TB between June 2005 and June 2006. Both initial and follow-up isolates were available for spoligotyping for 17 of these patients. In all cases, the follow-up isolates' spoligotypes differed from those of the initial isolate, indicating exogenous reinfection. Two genotypes (shared type [ST] 34 and ST 60, associated with MDR and XDR TB, respectively) were responsible for 85% of reinfections. All 17 patients had been hospitalized; all 15 whose HIV infection status was known were HIV-infected. CONCLUSIONS Exogenous reinfection is an important mechanism for the development of MDR and XDR TB. In addition to strengthening TB treatment programs, effective infection control strategies are urgently needed to reduce the transmission of MDR and XDR TB.