Mycobacterium avium-intracellulare complex (MAC) is a ubiquitous pathogen found in soil and water. Environmental exposure is the primary route for MAC infection. However, specific environmental risk factors have been poorly determined in immunocompetent patients with pulmonary MAC disease.
A case-control study was performed with 106 patients with pulmonary MAC disease (men [women], 23 ; age, 64.3 ± 9.2 years) and 53 age-matched control patients with bronchiectasis but not pulmonary MAC infection (men [women], 7; age, 63.0 ± 11.0 years). All participants completed a standardized questionnaire that included questions about medical history, smoking history, alcohol usage, age at menopause, and environment exposures. Environment exposures included soil exposure from farming or gardening; water exposure from bathing, showering, hot tub use, dishwashing, swimming, and drinking water; and pet exposure.
No differences were identified in the patient characteristics and underlying diseases. More case patients experienced high soil exposure (≥ 2 per week) than control patients (23.6% vs 9.4%, P = .032); this remained significant after multivariate analysis (OR, 5.9; 95% CI, 1.4-24.7; P = .015). There were no significant differences in other environmental exposures. Case patients with high soil exposure were significantly older than those with low soil exposure (67.3 ± 7.3 years vs 64.3 ± 9.5 years, P = .037). Other characteristics, underlying diseases, and mycobacterial species did not differ between the two groups.
Patients with pulmonary MAC disease had significantly more soil exposure than noninfected control patients, which suggests that environmental soil exposure is a likely risk factor for the development of pulmonary MAC disease.