Abstract
Rapidly growing mycobacteria (RGM) are respiratory pathogens in patients with cystic fibrosis (CF), but detection generally requires specialized cultures for acid-fast bacilli (AFB; AFB cultures). We determined that RGM could be recovered from routine cultures of samples from patients with CF by extending incubation of the Burkholderia cepacia selective agar (BCSA) from 5 to 14 days. To explore the impact of this modification, we compared results from routine and AFB cultures of samples from CF patients for 2 years before (4,212 samples by routine culture, 1,810 samples by AFB culture, 670 patients) and 2 years after (4,720 samples by routine culture, 2,179 samples by AFB culture, 695 patients) the change. Clinical relevance was assessed with samples from a subgroup of 340 patients followed regularly throughout both periods. Extending incubation of BCSA enhanced RGM recovery from routine cultures (0.7% before, 2.8% after; P < 0.001); recovery from AFB cultures was unchanged (5.5% before, 5.7% after). Estimates of RGM detection sensitivity by culture or patient-based methods ranged from ∼65 to 75% for routine cultures (nonsignificantly lower than the ∼80 to 85% for AFB cultures) and were adversely affected by coculture with mold or nonpseudomonal, nonfermenting Gram-negative rods. In the after period, 16 CF patients met the criteria for RGM infection by routine culture, including 4 who did not meet the criteria for RGM infection by AFB culture. We conclude that a simple methodological change enhanced recovery of RGM from routine cultures. The modified culture method could be utilized to improve screening for RGM in CF patients or as a simpler method to follow patients with known RGM infection. However, this method should be used cautiously in patients with certain coinfections.