Mycobacterium avium complex

Mycobacterium avium complex (MAC) has variable presenting features including chronic cough, weight loss, and fevers.

Increased incidence in patients with underlying lung disease, heavy smoking, and excessive alcohol consumption.

HIV-infected patients with CD4 cell count <50 cells/microlitre are also at increased risk of infection.

Diagnosis of pulmonary disease in non-HIV-infected individuals requires repeated isolation of the organism from respiratory secretions, in addition to compatible symptoms and radiographical presentation.

Combination treatment with at least two drugs is essential.

MAC, also known as Mycobacterium avium-intracellulare (MAI), consists of two mycobacterium species, M avium and M intracellulare.[1]Good RC. Opportunistic pathogens in the genus mycobacterium. Annu Rev Microbiol. 1985;39:347-69. http://www.ncbi.nlm.nih.gov/pubmed/3904604?tool=bestpractice.com Although MAC isolates can be identified as M avium or M intracellulare by molecular techniques, there is no prognostic or treatment advantage for doing so.[2]Saito H, Tomioka H, Sato K, et al. Identification of various serovar strains of Mycobacterium avium complex by using DNA probes specific for Mycobacterium avium and Mycobacterium intracellulare. J Clin Microbiol. 1990 Aug;28(8):1694-7. http://jcm.asm.org/cgi/reprint/28/8/1694?view=long&pmid=2203807 http://www.ncbi.nlm.nih.gov/pubmed/2203807?tool=bestpractice.com

In humans, MAC traditionally causes three disease syndromes: pulmonary disease, cervical lymphadenitis, and disseminated disease.[3]Rosenzweig DY. Pulmonary mycobacterial infections due to Mycobacterium intracellulare-avium complex. Chest. 1979 Feb;75(2):115-9. http://www.ncbi.nlm.nih.gov/pubmed/421545?tool=bestpractice.com [4]Wolinsky E. Mycobacterial lymphadenitis in children: a prospective study of 105 nontuberculous cases with long-term follow-up. Clin Infect Dis. 1995 Apr;20(4):954-63. http://www.ncbi.nlm.nih.gov/pubmed/7795100?tool=bestpractice.com [5]Horsburgh CR Jr, Mason UG, Farhi DC, et al. Disseminated infection with Mycobacterium avium-intracellulare: a report of 13 cases and a review of the literature. Medicine. 1985 Jan;64(1):36-48. http://www.ncbi.nlm.nih.gov/pubmed/3880852?tool=bestpractice.com ​ A fourth syndrome, a hypersensitivity pneumonitis associated with hot tub use, has also been described.[6]Rickman OB, Ryu JH, Fidler ME, et al. Hypersensitivity pneumonitis associated with Mycobacterium avium complex and hot tub use. Mayo Clin Proc. 2002 Nov;77(11):1233-7. http://www.ncbi.nlm.nih.gov/pubmed/12440560?tool=bestpractice.com