Diagnosis:
Nontuberculous Pulmonary Disease
• Mycobacterium avium complex (MAC) includes M. avium and M. intracellulare as well as several other less commonly isolated species.
• MAC is the most common cause of nontuberculous mycobacterial disease, causing lymphadenitis (usually in children), soft tissue infections, and disseminated disease in immunocompromised patients, such as HIV patients with a CD4+ count of less than 50/μL.
• Patients exposed to MAC present in recreational hot tubs may develop a hypersensitivity pneumonitis-like syndrome.
• The innate resistance to chlorination and ozonization compared to other nontuberculous mycobacteria may explain the high prevalence of MAC lung disease.
• Fibronodular bronchiectasis of the right middle lobe and lingua is a frequently seen manifestation of MAC disease in thin, elderly women. Cavitary lung disease involving the upper lobes, similar to pulmonary tuberculosis, can occur in older males with a history of tobacco or alcohol abuse.
• MAC colonial morphology is distinguished from other nontuberculous mycobacteria as shown in the table. It is a slow-growing, nonchromogen with detectable growth on solid media after 3 to 6 weeks and in liquid media after 1 to 2 weeks.
| Runyoun Classification of Nontuberculous Mycobacteria |
| Runyoun Group |
Classification |
Growth Rate |
Pigment Production |
| I |
Photochromogen |
Slow growing ≥ 7 days |
Colony pigment production occurs after exposure to light |
| II |
Scotochromogen |
Slow growing ≥ 7 days |
Pigment production in colonies is independent of the presence of light |
| III |
Nonphotochromogen |
Slow growing Greater than 7 days |
Nonpigmented colonies |
| IV |
Rapid-grower |
Rapid grower ≤ 7 days |
Mostly nonpigmented |
