[Clinical importance of Mycobacterium kansasii and evaluation of the need to identify nontuberculous mycobacteria].

BACKGROUND: The aim of this study was to evaluate the clinical importance of a single isolation of Mycobacterium kansasii in order to determine whether a single isolation of nontuberculous mycobacteria is sufficient to diagnose mycobacteriosis or whether multiple isolations are required, in which case, it would be better to wait until a second isolation is produced before undertaking identification of all nontuberculous mycobacteria.

PATIENTS AND METHODS: Between 1992-1998, we studied the characteristics of 77 isolates of M. kansasii because it is the nontuberculous mycobacterium most frequently associated with disease. Our hospital has 500 beds but processed the samples from the Principe de Viana Outpatient Center and those from the district hospitals of Tudela and Estella for mycobacteria. During the study period, a mean of 3,900 specimens were processed per year. The isolates came from 22 episodes in 21 patients (19 males and 2 females). The specimens were cultured using standard techniques and confirmation was performed using gene probes (Gen-Probe, San Diego, California).

RESULTS: Of the 22 episodes, positive cultures were obtained on multiple occasions in 15 (68.1%) and a single isolation was obtained in 7. All isolations came from respiratory samples. Isolations were obtained from blood on only 2 occasions (both in HIV-positive patients). Direct bacilloscopy was positive in 60% of cases with multiple isolations and negative in all cases of single isolation. Multiple isolations were found in 14 patients, 7 of whom were HIV-positive and with advanced immunodepression and 7 were HIV-negative. Of these, two were alcoholics and the remaining patients had chronic pulmonary diseases. All treated patients showed initial improvement after specific therapy and negative bacilloscopies and cultures. None of the patients with a single isolation, including two HIV-positive patients, showed clinical repercussions.

CONCLUSION: In our experience, a single isolation of M. kansasii was without clinical importance, even in two HIV-positive patients. Given that when the criteria of the American Thoracic Society for the diagnosis of mycobacteriosis are followed, in general, multiple mycobacteria should be isolated, a strategy of not undertaking the identification of all nontuberculous mycobacteria until a second isolation is produced can be established, unless there is serious clinical indication to suggest otherwise.