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Epidemiology of Mycobacterium kansasii

TO THE EDITOR: Bloch and colleagues (1) observed, as has previously been suggested (2), that Mycobacterium kansasii isolation is more common in HIV-positive persons. This interesting study provides additional information about the possible association between poverty and M. kansasii infection. However, the absence of microbiological and molecular characterization of the isolates in this study is a serious limitation. When M. kansasii is characterized by using standard methods, there is an impression that M. kansasii is a homogeneous group of organisms. However, the heterogeneity of M. kansasii has been reported and is well documented (3); every genotype described has different clinical significance (3, 4). Of the five subtypes identified, M. kansasii types I and II are frequent clinical isolates, while the remaining types are basically recovered from environmental samples (3). Type I is the most prevalent M. kansasii isolate from human sources worldwide (3-5), and its clonal structure suggests the possibility of a close relationship with men. Thus, the studies about clinical and epidemiologic implications of isolation of M. kansasii should consider this. Knowing which subtype or subtypes of M. kansasii are implicated with infection in different groups of persons (for example, persons who are HIV-positive, HIV-negative, or homeless or who are living in marginal housing) would solve many questions about the reservoir and mechanisms of transmission of these microorganisms. Bloch and colleagues' population-based study was a great opportunity to approach some of these issues, but the M. kansasii isolates were not extensively identified or subjected to molecular characterization. Therefore, we would like to draw attention to the importance of genotype definition of M. kansasii isolates for future epidemiologic, pathogenicity, and clinical studies of these infections.