Objective: The incidence of pulmonary Mycobacterium avium complex (MAC) infections with nodular/bronchiectasis lesions is increasing. However, factors determining deterioration are unknown. In the present study, we investigated quantitative MAC cultures obtained through bronchoscopic microsampling (BMS) from patients with pulmonary MAC infection and analyzed the relationship between MAC culture and the short-term natural history. We also assessed chest computed tomography (CT) findings for the deteriorating factors.
Design: For this prospective study, MAC was collected from peripheral lung lesions by BMS through endobronchial ultrasonography. MAC colonies were counted on Middlebrook 7H11 agar. We compared the number of MAC colonies with laboratory data and chest CT findings.
Patients: We studied 26 patients with pulmonary MAC infection.
Results: The patients were divided into 2 groups: 11 patients in the non-deteriorated group and 15 patients in the deteriorated group. The number of MAC colonies was significantly correlated with deterioration of MAC infection (p < 0.001). In the non-deteriorated group, chest CT scans showed nodular/bronchiectasis lesions in 8 patients (73%) and consolidated lesions in 3 patients (27%). In the deteriorated group, chest CT scans showed nodular/bronchiectasis lesions in 1 patient (7%), consolidated lesions in 6 patients (40%), and cavitary lesions in 8 patients (53%).
Conclusion: The number of MAC colonies in relevant lesions investigated by BMS was significantly larger in the deteriorated group than in the non-deteriorated group. Cavitary and consolidated lesions observed from chest CT scans are thought to indicate a high risk of progression of pulmonary MAC infection.