Clinical significance of the differentiation between Mycobacterium avium and Mycobacterium intracellulare in M avium complex lung disease

Background: Mycobacterium avium and Mycobacterium intracellulare are grouped together as the M avium complex;however, little is known about the clinical impact of this species differentiation. This study compared the clinical features and prognoses of patients with M avium and M intracellulare lung disease. Methods: From 2000 to 2009, 590 patients were given a new diagnosis of M avium complex lung disease; 323 (55%) had M avium lung disease, and 267 (45%) had M intracellulare lung disease. Results: Compared with the patients with M avium lung disease, the patients with M intracellulare lung disease were more likely to have the following characteristics: older age (64 vs 59 years, P =.002), a lower BMI (19.5 kg/m² vs 20.6 kg/m ², P<.001), respiratory symptoms such as cough (84% vs 74%, P =.005), a history of previous treatment for TB (51% vs 31%, P<.001), the fibrocavitary form of the disease (26% vs 13%, P<.001), smear-positive sputum (56% vs 38%, P<.001), antibiotic therapy during the 24 months of follow-up (58% vs 42%, P<.001), and an unfavorable microbiologic response after combination antibiotic treatment (56% vs 74%, P =.001). Conclusions: Patients with M intracellulare lung disease exhibited a more severe presentation and had a worse prognosis than patients with M avium lung disease in terms of disease progression and treatment response. Therefore, species differentiation between M avium and M intracellulare may have prognostic and therapeutic implications.