Non-tuberculous mycobacteria in cystic fibrosis

BACKGROUND—The clinical significance of thepresence of non-tuberculous mycobacteria in the sputum of patients withcystic fibrosis is unclear. A retrospective case-control study wasperformed to assess possible risk factors for non-tuberculousmycobacteria and its impact on clinical status in patients with cystic fibrosis.
METHODS—The records of all patients attending theLeeds cystic fibrosis clinics who were positive for non-tuberculousmycobacteria were examined. Each case was matched with two controls forsex, age, and respiratory function at the time of the firstnon-tuberculous mycobacteria isolate. Details of respiratory function,nutritional status, antibiotic and corticosteroid therapy,Shwachman-Kulczycki (S-K) score, Northern chest radiographic score, andthe frequency of isolation of other bacteria and fungi were collectedfrom two years before to two years after the first non-tuberculousmycobacteria isolate. The patients' genotype and the presence ofdiabetes mellitus were also recorded.
RESULTS—Non-tuberculous mycobacteria were isolatedfrom 14 patients out of a cystic fibrosis population of 372 (prevalence = 3.8%). No significant effect of non-tuberculous mycobacteria wasseen on respiratory function, nutritional status, or S-K score. There was a significant association with the number of intravenous antibiotic courses received before the first isolate with cases receiving, onaverage, twice as many courses as controls (cases 6.64, controls 2.86, 95% CI for difference 1.7 to 5.9). No significant difference was seenbetween cases and controls for Northern scores, previous steroidtherapy, or the incidence of diabetes mellitus.
CONCLUSIONS—Non-tuberculous mycobacteria infectionin patients with cystic fibrosis is uncommon and its clinical impactappears to be minimal over a two year period. Frequent intravenousantibiotic usage is a possible risk factor for colonisation withnon-tuberculous mycobacteria.