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In November 2006, investigators reported a highly fatal outbreak of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB) in a rural subdistrict of KwaZulu-Natal, South Africa, that has a high prevalence of HIV infection (AIDS Clin Care Nov 13 2006). Although most cases of drug-resistant TB worldwide are believed to result from failure of TB therapy, many patients in this particular outbreak had not received such therapy previously, and those who had showed resistance to drugs that they had never received. Many of the cases were therefore believed to be due to reinfection with a resistant strain of TB.
To test this hypothesis, investigators reviewed data from 17 patients with MDR- or XDR-TB who had previously received treatment for culture-positive, drug-susceptible TB. Fifteen of the patients were known to be HIV-infected; the HIV status of the other 2 patients was unknown. Primary drug resistance due to exogenous reinfection was distinguished from acquired drug resistance by comparing genotypes of the drug-sensitive isolates from the first TB episodes (obtained at treatment initiation) with genotypes of isolates from the second episodes. Differences in the spoligotyping patterns between the initial and follow-up isolates from all 17 patients indicated exogenous reinfection with a drug-resistant organism.
Andrews JR et al. Exogenous reinfection as a cause of multidrug-resistant and extensively drug-resistant tuberculosis in rural South Africa. J Infect Dis 2008 Oct 10; [e-pub ahead of print].
Comment
Current efforts to prevent drug-resistant TB focus on directly observed treatment, short course (DOTS), based on the assumption that, in most cases, resistance emerges as a result of treatment nonadherence. However, this study makes clear that such efforts alone will not slow the spread of drug-resistant TB in areas like rural South Africa that have a high prevalence of both HIV and TB infection. Public health efforts must therefore be expanded to prevent the transmission of drug-resistant Mycobacterium tuberculosis strains, particularly in AIDS treatment programs. Such programs create multiple opportunities for person-to-person spread of TB by bringing together large numbers of patients in waiting rooms, patient queues, and public transport to hospitals. At a minimum, AIDS treatment clinics must improve infection-control measures and implement protocols for intermittent preventive therapy with isoniazid.