A recent study has found that most cases of drug-resistant tuberculosis among patients undergoing treatment for the disease may reflect new infections, not acquired resistance (Li X et al. J Infect Dis. 2007;195:864-869). The findings run counter to the common belief that drug resistance among treated patients is acquired through mutations in the infecting Mycobacterium tuberculosis strain.
By genotyping the initial and subsequent drug-resistant clinical isolates of M tuberculosis collected from patients over the course of a 5-year period, investigators at the Shanghai Medical College, in China, found that 84% of patients (27 of 32) had primary drug resistance, indicating transmission of a drug-resistant strain of M tuberculosis. Only 16% (5 of 32) had acquired drug resistance because of a poor treatment regimen or nonadherence to an adequate regimen. Thus, there were more than 5 times as many cases caused by reinfection than by genetic changes within M tuberculosis.
Hampton T. Tuberculosis Resistance. JAMA. 2007;297(13):1423. doi:10.1001/jama.297.13.1423-c