Atypical Mycobacterial Avium Intracellulare Infection in the Immunocompetent Host

Abstract Introduction : Mycobacterium avium complex (MAC) is a gram-positive acid-fast bacillus that is the most common cause of non-tuberculosis mycobacterial pulmonary disease (NTM-PD). Acquisition of MAC is via inhalation; thus making the pulmonary system the most common site of infection. Prevalence of MAC infections in the United States varies from 1.4-6.6 per 100,000 individuals and can be found in soil, water, and dust. Risk factors for MAC include chronic lung disease, CD4 count less than 50 in AIDS patients, and immunosuppression. Dissemination of MAC can occur in those with AIDS and immunosuppression. Case : We present a 38-year-old female with a history of tobacco use who was referred to Pulmonology for abnormal computed tomography (CT) findings. History revealed the patient returned from Tanzania in November 2023 and a nonproductive cough started then. Initially the patient had no associated symptoms; but she later on developed night sweats and dyspnea. CT chest revealed right upper lobe cavitary lesion measuring up to 4.1 cm with bilateral tree-in-bud nodularities and prominent nodules in the right lower lobe measuring up 1.6 cm in maximal dimension. A Quantiferon test was negative. Navigational bronchoscopy performed in April 2024 revealed no evidence of malignancy; however, there was evidence of granulomatous changes. Acid-fast bacilli culture grew Mycobacterium Avium intracellulare. The patient was referred to Infectious Disease and started on daily azithromycin 500 mg, rifampin 600 mg, and ethambutol 900 mg. Decision was made to add intravenous (IV) amikacin twice a week. Duration of oral antibiotics will be for 18 months and IV antibiotics for 2-3 months. Discussion: This case highlights an interesting and rare phenomenon of MAC lung disease in an immunocompetent host. MAC is typically seen in individuals who are immunocompromised, have underlying lung disease, or of elderly age; none of which our patient exhibits. The patient was likely exposed during her travels abroad. There are two types of MAC lung disease: nodular bronchiectatic and fibrocavitary disease. Nodular bronchiectatic type develops in the small airways and is typically seen in females who do not smoke. Fibrocavitary disease type is the more severe form of MAC due to its cavitary nature and is typically seen in individuals who smoke or have emphysema. MAC infection can appear similar to tuberculosis (Tb) on imaging; however, causative agent and diagnosis modality is different. Identification of MAC lung disease is important to prevent disseminated MAC; especially in at-risk populations as complications can lead to death.