Simultaneous infection with two drug-susceptible Mycobacterium tuberculosis strains in an immunocompetent host

An important assumption for DNA fingerprinting of Mycobacterium tuberculosi s is that patients are infected with only one strain at a time. Nonetheless , we demonstrate a case of simultaneous infection with two drug-susceptible strains of M. tuberculosis in an immunocompetent patient by IS6110 restric tion fragment length polymorphism and spoligotyping. Epidemiological data p rove the patient's involvement in two independent clusters. Thus, double in fections should be suspected with fingerprints showing divergent band inten sities.