5. 8 MAI and MAC

Type of infection

Mycobacterium avium and Mycobacterium intracellulare are two bacterial organisms closely related to Mycobacterium tuberculosis which causes TB.

Illness from these bacteria is called MAI in Europe and MAC in the US, but they are the same.

A CD4 count under 100 cells/mm³ increases the risk for MAI. The lower your CD4 count the higher the risk.

Infection comes from soil, dust or contaminated water, but is not infectious between individuals.

MAI can spread throughout the body. It can affect almost any organ, especially the blood, lymph nodes, liver, spleen and bone marrow. The cells infected by these bacteria include macrophages (white blood cells that engulf infectious material).

Main symptoms

Blood tests can show low levels of red blood cells (anaemia) and platelets (thrombocytopenia).

Diagnosis

MAI is confirmed by growing a culture from blood or samples from the affected part of the body. This can take up to four weeks.

An ‘acid smear’ test is much quicker but cannot tell the difference between MAI and TB.

Treatment

Treatment involves a combination of 2 or more antibiotics (to reduce the risk of resistance) – usually clarithromycin or azithromycin plus ethambutol.

People who develop resistance to clarithromycin will also have resistance to azithromycin and vice versa. Other drugs used in combinations include rifabutin rifampicin, gentamicin, amikacin, ciprofloxacin and sparfloxacin.

If ARVs increase CD4 count above 100 cells/mm³ treatment can be safely stopped after 1 year. Otherwise, treatment is life-long.

Prophylaxis

It is unclear if prophylaxis is needed for people with CD4 counts under 50 cells/mm³. Recommendations vary in different countries.

ARVs are likely to be more protective, as they will increase the CD4 count to a safe level.

Clarithromycin and azithromycin, taken correctly, reduce the risk of MAI by about 70%. But if MAI occurs while taking either of these antibiotics, the infection may be resistant to treatment by both of them.