Molecular genotyping has shown Mycobacterium tuberculosis lineages to be geographically restricted and associated with distinct ethnic populations. Whether tuberculosis (TB) caused by some M. tuberculosis lineages can present with a differential clinical spectrum is controversial because of very limited clinical data. We recently reported on the discovery of RD Rio M. tuberculosis, a Latin American-Mediterranean sublineage that is the predominant cause of TB in Rio de Janeiro, Brazil. To investigate the clinical attributes of TB caused by RD Rio strains, we studied a cohort of TB cases from Belo Horizonte, Brazil, in which clinical information recorded on a standardized questionnaire was collected at the time of microbiological testing. These patients were referred for culture and drug susceptibility testing because of the clinical suspicion of "complicated" TB, as demonstrated by high rates of multidrug resistance (12%) and cavitary TB (80%). We performed spoligotyping and RD Rio genotyping on the M. tuberculosis strains and analyzed the clinical data from these patients. RD Rio M. tuberculosis accounted for 37% of the total TB burden. Multivariate analysis found a significant association between TB caused by RD Rio strains and pulmonary cavitation and residence in Belo Horizonte. Since cavitary TB is associated with higher sputum bacillary load, our findings support the hypothesis that RD Rio M. tuberculosis is associated with a more "severe" disease as a strategy to increase transmission. Future studies are needed to confirm these observations and to better define the contribution of RD Rio M. tuberculosis to the global TB epidemic.Mycobacterium tuberculosis, the etiologic agent of tuberculosis (TB), is estimated to have infected one-third of the world's population and annually causes ϳ8 million new TB cases and Ͼ2 million deaths (16, 58). The challenges posed by TB have been further worsened by the emergence of multi-drugresistant and extensively drug-resistant M. tuberculosis strains.Molecular typing, based on genetic markers, permits the rapid detection and species level identification of mycobacteria within the M. tuberculosis complex (MTC), as well as provides useful tools for examining the transmission and evolution of these microorganisms (7,17,30,53). Genome-wide single nucleotide polymorphism (SNP) and deletion analyses have been used to organize the global M. tuberculosis population structure into overlapping phylogenies with major lineages that show distinct geographic distribution and that may be associated with specific host adaptation (1,21,23,24,27,28,50). Similar results have also been obtained with spoligotyping and IS6110-RFLP fingerprint analysis (18). The W/Beijing lineage, for example, is the predominant family in major SNP cluster II, accounts for ϳ10% of strains causing TB globally, and is localized mainly to Asia but has spread internationally. W/Beijing has been associated with outbreaks and multiple drug resistance (MDR) (4, 32) and also contributed significantly to the resurgence of...