Bakula Z, et al. - Researchers retrospectively assessed features of patients from whom M. kansasii respiratory isolates were recovered and described M. kansasii disease in detail. In patients with M. kansasii disease compared to M. kansasii isolation, as classified using the American Thoracic Society and Infectious Diseases Society of America (ATS/IDSA) diagnostic criteria, significantly higher proportion of positive smear microscopy was detected. Clinical symptoms or comorbidities did not statistically significantly differed between these two groups of patients. Overall, the relaxation of the diagnostic criteria for the definition of M. kansasii disease, set forth by ATS/IDSA, was supported. The role of bacterial virulence factors remained elusive as molecular typing failed to distinguish isolates from patients with true disease from those with isolation only.