Association between polyclonal and mixed mycobacterial Mycobacterium avium complex infection and environmental exposure.

RATIONALE

Polyclonal and mixed mycobacterial Mycobacterium avium complex (MAC) infection is observed in pulmonary MAC disease. Human living environments contain multiple species or genotypes of nontuberculous mycobacterial strains and are considered sources of infection.

OBJECTIVES

To investigate the association of environmental exposure with polyclonal and mixed mycobacterial infection in pulmonary MAC disease after adjustments for potential confounding diseases and conditions and radiographic findings.

METHODS

We collected two separate sputum samples from 102 patients and single sputum samples from 18 patients in whom the second MAC strain was not isolated in our prospective cohort of pulmonary MAC disease. MAC isolates from sputum samples and patients' residential soils were used for variable number of tandem repeats (VNTR) analyses. Polyclonal and mixed mycobacterial MAC infections were defined as having different VNTR genotypes and other mycobacterial species, respectively. Monoclonal MAC infection was defined as all isolates showing a single VNTR genotype. Associations of the type of infection with clinical and radiographic findings and environmental exposure were measured.

MEASUREMENTS AND MAIN RESULTS

Polyclonal and mixed mycobacterial MAC and monoclonal infections were observed in 42 and 78 patients, respectively. By stepwise regression analysis, patients with polyclonal and mixed mycobacterial MAC infections were associated with history of asthma (odds ratio [OR], 11.56; 95% confidence interval [CI], 1.41-255.77; P = 0.021), high soil exposure (≥2 h/wk; OR, 4.31; 95% CI, 1.72-11.45; P < 0.01), shower use in a bathroom (OR, 4.57; 95% CI, 1.28-23.23; P = 0.018), and swimming in a pool (OR, 9.69; 95% CI, 1.21-206.92; P < 0.01).

CONCLUSIONS

Environmental exposure was associated with polyclonal and mixed mycobacterial MAC infection in pulmonary MAC disease.