Double infection with a Resistant and a Multidrug-Resistant Strain of Mycobacterium tuberculosis

During the last decade, drug-resistant Mycobacterium tuberculosis (TB) strains have emerged, posing a major threat to global TB control efforts. The incidence of drug-resistant TB has increased in many parts of the world, not only in developing countries but also in industrialized countries, where the prevalence of drug-resistant TB had been low (1). The emergence of drug resistance during antituberculous therapy results mainly from inadequate therapy, i.e., improper prescription of treatment regimens, addition of single drugs to failing treatment regimens, and patient noncompliance. However, inconsistent drug-susceptibility patterns or delayed responses to TB therapy may also indicate exogenous reinfection with a strain resistant to multiple drugs or mixed infection with a sensitive and a multidrug-resistant TB strain. Such infections occur in immunocompromised and immunocompetent persons (2-7) and may be more common in areas with high prevalence of resistant TB