Outcome of patients with and poor prognostic factors for Mycobacterium kansasii-pulmonary disease

Background: Aggressive therapy for Mycobacterium kansasii-pulmonary disease (MK-PD) is recommended because of the virulence of MK. However, some clinicians may be concerned regarding the lengthy course and numerous adverse effects. This study evaluated the natural course of MK-PD and investigated its prognostic factors. Methods: Radiographic outcome, prognostic factors, and mortality within 1 year for MK-PD were obtained from patients in 6 hospitals in Taiwan from 2010 to 2014 (derivation cohort) and validated using patients in 2015 and 2016 (validation cohort). Results: Of the 109 patients with MK-PD in the derivation cohort, radiographic progression occurred in 70 (64%), with a 1-year mortality rate of 43% and median survival of 71 days, whereas none of the 39 cases without radiographic progression died. All patients with acid-fast smear (AFS) grade >= 3 experienced radiographic progression. For the others, the independent risk factors of radiographic progression were fibroCavitary pattern, Leucocyte count>9000/mu L, Old age (age>65 years), pUre MK in sputum (no other mycobacteria), and no Diabetes mellitus (the CLOUD factors). By applying these criteria to the validation cohort (n=112), 3 (9%) of the 33 patients with MK-PD who initially had AFS grade < 3 and < 3 CLOUD risk factors experienced radiographic progression, and none of the 3 died of MK-PD. Conclusions: Because of the high risk of radiographic progression and subsequent fatal outcome, immediate anti-MK treatment is recommended. For patients with MK-PD who have sputum AFS grade < 3 and < 3 CLOUD risk factors, regular follow-up may be an alternative.