Clinical significance of a first positive nontuberculous mycobacteria culture in cystic fibrosis.

RATIONALE: Little is known about outcomes of infection with nontuberculous mycobacteria (NTM) in cystic fibrosis (CF) or about the significance of a positive NTM culture. Determining which patients are at risk for active NTM disease is clinically valuable.
OBJECTIVES: To examine the clinical course of subjects with CF with an initial positive NTM culture and identify characteristics associated with active NTM disease.
METHODS: We performed a retrospective study of pediatric and adult subjects with CF with at least one positive NTM culture at the Colorado CF Center from 2000 to 2010.
MEASUREMENTS AND MAIN RESULTS: Mycobacterium avium complex was the first identified NTM in the majority of subjects (73%). The frequency of growing a second NTM species was 26% at 5 years. Clinical characteristics and distribution of NTM species between pediatric and adult subjects were similar except for differences in baseline FEV1 (89% vs. 71%; P < 0.001) and coinfection with Pseudomonas aeruginosa (33% vs. 55%; P = 0.04). Over 60% of subjects had transient or persistent infection but not active NTM disease. Subjects who developed active NTM disease were distinguished from those with transient or persistent infection, respectively, by FEV1 at the time of first positive NTM culture (72% vs. 84 or 86%; P = 0.02) and FEV1 decline in the prior year (-5.8%/yr vs. -0.7%/yr [P = 0.009] or -0.4%/yr [P = 0.001]).
CONCLUSIONS: The majority of patients with CF with a first positive NTM culture do not progress to active disease. Lower lung function and accelerated lung function decline appear to be indicators of the significance of an initial positive NTM culture.