View source for Mycobacterium avium complex

== Background ==
=== Microbiology ===
* A slow-growing [[non-tuberculous mycobacterium]]
* Comprises ''M. avium'' (subspecies ''hominissuis'' in humans) and ''M. intracellulaire''
** 28 serovars between the two
* Can colonize airways and GI tract as well as causing disease

=== Differential Diagnosis ===
* Pulmonary disease
** ''M. kansasii''
** ''M. abscessus''

=== Epidemiology ===
* Common in the environment, likely acquired by inhalation or ingestion (not person-to-person)
** Water, soil, and animals
** Natural water, indoor water, pools, hot tubs
* Risk factors
** Pulmonary disease: [[COPD]], prior [[pneumonia]], prior [[TB]], [[Corticosteroids|steroid]] use, [[silicosis]], [[scoliosis]], [[pectus excavatum]]
** Disseminated disease: [[HIV]], interferon-gamma defects
** [[Cervical lymphadenitis]]: children 1-5 years old, [[HIV]] with [[IRIS]]

=== Pathophysiology ===
* In pulmonary disease, likely inhalation ± microaspiration
* In disseminated disease in [[AIDS]], likely GI colonization then replication and dissemination

== Clinical Manifestations ==
=== Pulmonary disease ===
* Incubation period [[Usual incubation period::months to years]]
* Typically presents with non-specific subacute to chronic respiratory syndrome
** Productive cough, weight loss, fevers, night sweats
* CXR often shows upper-lobe infiltrates ± cavitations ± pleural thickening
** Bronchiectasis on CT in 94%
* Mortality is 15% within 2 to 10 years
* Specific populations/presentations:
** Smokers/COPD/alcohol: typical presentation as above
** Lady Windermere syndrome: slower progression
** Hot tub lung disease: a hypersensitivity pneumonitis associated with inhalation

=== Disseminated disease ===
* Almost exclusive to HIV patients with CD4 &lt;100
** Median CD4 was 13
* Typically presents with high fevers, weight loss, night sweats, anemia
* Also abdo pain, diarrhea, intraabdo lymphadenopathy, hepatosplenomegaly, and elevated ALP
* Organ-specific involvement: spleen, lymph nodes, liver, adrenals, stomach, CNS
** Often ''not'' lung involvement
* Mortality 50% at 4 months

=== Cervical lymphadenitis ===
* Disease of children, usually &lt;3 (80% aged 1 to 5 years)
* Presents as painless unilateral lymph node enlargement
** 10% bilateral

== Investigations ==
=== Pulmonary disease ===
* (1) chest radiograph or, in the absence of cavitation, chest high-resolution computed tomography (HRCT) scan
* (2) three or more sputum specimens for acid-fast bacilli (AFB) analysis
* (3) exclusion of other disorders, such as tuberculosis

== Diagnosis ==
=== Pulmonary disease ===
* Diagnosis based on presence of both clinical and microbiological evidence
* Clinical:
** Pulmonary '''symptoms''', nodular or cavitary opacities on '''chest radiograph''', or an HRCT scan that shows multifocal bronchiectasis with multiple small nodules; and
** Appropriate exclusion of other diagnoses.
* Microbiological:
** Positive cultures from at least two separate expectorated sputum samples; or
** Positive culture from at least one bronchial wash or lavage; or
** Transbronchial or other lung biopsy with mycobacterial histopathologic features, and either positive culture for NTM or one or more sputum or BALs positive for NTM

=== Disseminated disease ===
* Diagnosis based on MAC in culture of sterile site

== Management ==
=== Pulmonary disease ===
* Nodular/bronchiectatic disease:
** [[Clarithromycin]] (1,000 mg) or [[azithromycin]] (500 mg)
** [[Rifampin]] (600 mg)
** [[Ethambutol]] (25 mg/kg)
** Three times weekly (because daily never tolerated)
* If fibrocavitary MAC lung disease or severe nodular/bronchiectatic disease:
** [[Clarithromycin]] (500–1,000 mg) or [[azithromycin]] (250 mg) daily
** [[Rifampin]] (600 mg) or [[rifabutin]] (150–300 mg) daily
** [[Ethambutol]] (15 mg/kg) daily
** And consider adding three-times-weekly [[amikacin]] or [[streptomycin]] early in therapy
* Duration is until culture negative on therapy for at least 1 year
* Refer to Ophthalmology for monitoring while on [[ethambutol]]

=== Disseminated disease ===
* Antibiotics
** [[Clarithromycin]] (1,000 mg/d) or [[azithromycin]] (250 mg/d)
** [[Ethambutol]] (15 mg/kg/d)
** ± [[rifabutin]] (150–350 mg/d)
* Duration is until resolution of symptoms and reconstitution of cell-mediated immune function (e.g. CD4 &gt;100)

=== Prophylaxis ===
* Indicated for adults with (AIDS) with CD4 &lt;50; but not done and no longer in the HIV guidelines
* Antibiotics: [[azithromycin]] 1,200 mg/week or [[clarithromycin]] 1,000 mg/day
* Second-line: [[rifabutin]] 300 mg/day (less well tolerated)

{{DISPLAYTITLE:''Mycobacterium avium'' complex}}
[[Category:Non-tuberculous mycobacteria]]