intracellulare

Mycobacterium intracellulare is a species of non-tuberculous mycobacteria within the Mycobacterium avium complex (MAC). Like other MAC bacteria, M. intracellulare is found in the environment, including soil and water, and is typically acquired through inhalation or ingestion. In most people, exposure does not cause disease; infection tends to occur in individuals with underlying lung disease, reduced immune function, or both.

In the lungs, M. intracellulare can cause pulmonary disease that resembles tuberculosis, with symptoms such as chronic cough, fatigue, and weight loss, and radiographic findings that may include nodules, bronchiectasis, or fibrocavitary lesions. Two main syndromes are described in MAC lung disease: a fibrocavitary form more common in older men with a smoking history or COPD, and a nodular bronchiectatic form seen in some women without a prior smoking history.

In people with advanced immunosuppression, notably those with AIDS and low CD4 counts, M. intracellulare can cause disseminated MAC infection, presenting with fever, night sweats, weight loss, anemia, hepatosplenomegaly, and multiorgan involvement. It is an opportunistic pathogen in this setting.

Diagnosis relies on microbiology: repeatedly positive cultures for MAC organisms from sputum, bronchoalveolar lavage, or tissue, supported by imaging findings. Species-level identification distinguishes M. intracellulare from M. avium and other MAC members; molecular methods such as sequencing can aid confirmation.

Treatment typically involves a macrolide (azithromycin or clarithromycin) plus ethambutol and a rifamycin, often for 12 months after culture conversion. Additional agents may be used for disseminated disease, and treatment duration is prolonged. Drug susceptibility testing is not consistently predictive for MAC. Prognosis varies; disseminated disease can improve with effective immune restoration, such as antiretroviral therapy in AIDS, but MAC infection generally requires long-term management.