Mycobacterial infections

Mycobacterium avium complex consists of multiple nontuberculosis mycobacterial species (NTM), which cannot be distinguished in the microbiology laboratory and requires genetic testing. M. avium and Mycobacterium intracellular are the two original members of this complex, known for about a hundred years. Mycobacterium chimaera has been included in the M. avium intracellulare complex (2004). Some include Mycobacterium subspecies paratuberculosis in the My.avium complex as well. A newcomer to the Mycobacterium avium complex is the Mycobacterium paraintracellulare, identified in pulmonary infections in Southeast Asia in 2016. M. avium was first isolated in chickens 1933 with a cavitary disease resembling tuberculosis. Human cases were identified decades later. M. avium complex is the most common cause of nontuberculosis mycobacterial species infections in humans, and respiratory system is the most common site of infection. [1]

 

Multiple NTM in MAC

M. paratuberculosis

M. avium

M. intracellular

M. chimaera

M. paraintracellulare

There is no need to treat all patients with sputum positive for Mycobacterium avium complex. Selecting patients for therapy is a clinical calculus combining, microbiologic, radiologic and clinical criteria. The therapy is long, and there is significant potential for adverse drug reactions. [1]

The macrolide antibiotic is the backbone of therapy for Mycobacterium avium complex infections. The Infectious Disease Society of America recommended triple antibiotic therapy for fibro cavitary and severe nodular bronchiectatic disease. For moderate to mild disease, dual antibiotic therapy is sufficient. Observation is reasonable but in general Mycobacterium avium complex pulmonary infections are progressive, and eventually, a patient will have indications for therapy. In this situation, expert opinion suggests, that sputum should be checked once in three months and radiological evaluation once in six months. A chest x-ray may be sufficient for the fibro-cavitary disease, but HRCT is needed to assess nodular bronchiectatic disease. [1]

Risk factors for progressive MAC disease [1]