In AIDS patients and similarly immune-compromised patients, MAI becomes disseminated, with large accumulations of mycobacterium, the patient is bacteriemic and the bone marrow becomes infected. Mycobacterium marinum can cause swimming pool granuloma. It is found in water. Results in an ulcerating, chronic, lesion on hands that does not heal. This is treatable, but must be identified first.
Atypical mycobacteria are still disease causing, and are becoming more prevalent.
This depends upon interaction of host and infecting organism. It used to be that MAI was considered a contaminant of tissue cultures from humans. We now know that we don't really know much at all about what can and cannot be a pathogen. MAI and many other organisms can and are pathogenic given the correct circumstances and virulence factors. If you have an intact immune system MAI is not a pathogen, if you don't, it is.