Epidemiology

The prevalence of non-tuberculous mycobacterial (NTM) infections, including infections caused by Mycobacterium avium complex (MAC), is difficult to estimate, because they are not notifiable diseases in most countries and systematic surveillance and reporting mechanisms are lacking. Additionally, their diagnosis and the significance of their identification in culture is not always straightforward. As a result, reliable and accurate estimates of the incidence and prevalence of NTM infections are not available. There is general agreement that there is an increase in NTM (and MAC) infection and disease, however, it is unknown whether this is representative of a true increase in disease burden or rather increased awareness, improved diagnostics or an increase in predisposing host factors.[9][10][11]​​​​[12]

MAC lymphadenitis is primarily a disease of children, with approximately 300 cases reported annually in the US.[13][14]​​

Patients with healthy immune systems rarely develop illness as a result of MAC. However, in people with HIV, MAC can spread widely and affect almost any organ (especially the liver, spleen, and bone marrow). Prior to the availability of antiretroviral therapy (ART), disseminated MAC occurred in 20% to 40% of people with AIDS.[15] However, since the introduction of effective ART, the overall incidence of MAC disease among people with HIV has declined substantially to less than 2 cases per 1,000 person-years, even among those not receiving effective ART.[8]​ While the risk of MAC disease has decreased, it can still occur in people with HIV on suppressive ART. The presentation may differ from that seen in people with untreated HIV, with more localised diseases such as pneumonia, lymphadenitis, skin and soft tissue abscesses, and osteomyelitis rather than disseminated disease.[8]​​

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