Genetic relatedness of Mycobacterium avium-intracellulare complex isolates from patients with pulmonary MAC disease and their residential soils.

Mycobacterium avium-intracellulare complex (MAC) strains were recovered from 48.9% of residential soil samples (agricultural farms (n = 7), residential yards (n = 79), and planting pots (n = 49)) of 100 pulmonary MAC patients and 35 non-infected control patients. The frequency of MAC recovery did not differ among soil types or among patients regardless of the presence of pulmonary MAC disease, infecting MAC species or period of soil exposure. Variable numbers of tandem repeats (VNTR) analysis for MAC clinical and soil isolates revealed 78 different patterns in 47 M. avium clinical isolates and 41 soil isolates, and 53 different patterns in 18 M. intracellulare clinical isolates and 37 soil isolates. Six clinical and corresponding soil isolate pairs with an identical VNTR genotype were from case patients with high soil exposure (≥2 h per week, 37.5% (6/16) with high exposure compared with 0.0% (0/19) with low or no exposure, p <0.01), suggesting that residential soils are a likely source of pulmonary MAC infection.