Pulmonary Mycobacterium avium complex (MAC) infection may represent the next major health concern for immunocompromised patients; however the exact pathogenesis remains largely unknown. Current therapy consists of combined antibiotic treatment but bacterial eradication is frequently unsuccessful and the appearance of macrolide-resistant non-tuberculous mycobacteria (NTM) strains is cause for concern. In other mycobacterial disease such as tuberculosis (TB), infected mononuclear cells secrete soluble factors capable of driving unopposed secretion of proteolytic enzymes from stromal cells, which appears to be a causative factor for matrix degradation and progressive cavitary lung disease. As the pathophysiology of pulmonary MAC…show more content… The route of transmission for MAC is via inhalation or ingestion; thus this complex is capable of causing pulmonary or gastrointestinal disease, which frequently becomes disseminated systemically (6). Due to their presence in the environment, MAC infections are relatively common, yet rarely pathogenic (5).
Pulmonary NTM disease is an emerging infection with increasing incidence and morbidity, occurring mainly in areas with decreasing prevalence of TB (1, 7-9). This changing epidemiology may be attributed to an increasing prevalence of the susceptible host; as the survival of ‘at-risk’ patient groups is increasing, owing to improvements in medical health care. A previous lack of accurate diagnosis due to unawareness of NTM disease may also be attributed to this trend, and finally, a potential decrease in cross-protective herd immunity due to reduced exposure to TB and/or the dimished use of Bacillus Calmette–Guérin (BCG) vaccination may r contributing factors (1, 10).
Patients at risk of developing a MAC-associated lung disease are those with pre-existing pulmonary conditions, such as chronic obstructive pulmonary disease (COPD), bronchiectasis or cystic fibrosis, or those with systemic immunosuppression, such as human immunodeficiency virus (HIV) infection, cancer, inherited immune disorders, or those taking immunosuppressive drugs (1, 5,