Impact of chronic co-infection in pulmonary Mycobacterium avium complex disease after treatment initiation

Abstract Background: The impact of co-infection with other pathogenic microorganisms after initiation of treatment for pulmonary Mycobacterium avium complex (MAC) disease has not been clearly demonstrated. This study sought to clarify clinical outcomes of co-infection with MAC after antimycobacterial therapy for MAC.Methods: Co-infection status was designated as the detection of pathogenic microorganisms other than MAC in at least two consecutive sputum cultures 6-24 months after initiation of treatment. Chest computed tomography (CT) findings and culture results were compared between co-infection and MAC alone groups. Results: The co-infection and MAC alone groups comprised 12 and 36 patients, respectively. The proportion of patients with sputum culture positive for MAC after 24 months of therapy did not differ significantly between the two groups [25% (3/12) vs. 16.7% (6/36); p =0.671]. The proportion of patients with improved chest CT score after 24 months of starting treatment compared to baseline was significantly lower for the co-infection group than for the MAC alone group [16.7% (2/12) vs. 79.4% (27/34); p <0.001]. In the co-infection group, mean CT score values at 12 and 24 months did not differ from baseline. However, the MAC alone group showed significant improvement at 12 and 24 months compared with baseline.Conclusions: Co-infection with other pathogenic microorganisms has no effect on the therapeutic efficacy of MAC but interferes with improvement in chest CT findings.