INTRODUCTION: The purpose of this study was to separate MAC lung disease from 
colonization and to define indications for treatment.
MATERIALS AND METHODOLOGY: Over 4 years, we evaluated patients who had positive 
MAC cultures, MAC infection and coinfection with MTB. In the first study, 42 
immunocompetent patients with sputum or BAL culture positive only for MAC during 
a single year (2004) were reviewed. On clinical and radiographic review, they 
were classified as disease related to MAC, likely related to MAC or unrelated to 
MAC. In the second study, we reviewed all immunocompetent patients, during two 
years (2004-2005), whose respiratory secretions cultured both MTB and 
nontuberculous mycobacteria (NTM). In the last study, we evaluated pulmonary 
function (PF) in patients with MAC infection before and after therapy (2006- 
2007). PF was evaluated in patients following ATS guidelines.
RESULTS: Lung disease was related/likely related to MAC in 21 patients (50%) and 
not related in 21 (50%). In patients with MAC-related lung disease, the primary 
physician did not consider the diagnosis except when that physician was a 
pulmonologist. Half of those with MAC-related lung disease were smokers, white 
and US-born. There were 12 immunocompetent patients with MTB and NTM cultures. 
Eleven were non-white and all were foreign-born. Presentation and clinical 
course were consistent with MTB. All 8 patients with abnormal PF improved.
CONCLUSIONS: The prevalence of MAC lung infection in two inner city hospitals 
was four times higher than that of TB. The indication for treatment of MAC 
infection should also rely heavily on clinical and radiological evidence when 
there is only one positive sputum culture. The diagnosis was considered only 
when the admitting physician was a pulmonologist. Most patients with combined 
infection were clinically consistent with MTB and responded to anti MTB 
treatment alone. Treatment with anti-MAC therapy improved PF in those patients 
whose PF was abnormal to begin with.