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Mycobacterium avium-complex (MAC, Mycobacterium avium intracellulare, MAI)

Etiology: (risk Factors) 1) immunodeficiency (most commonly AIDS) - HIV1 infection with CD4 count < 50/uL [3] 2) underlying pulmonary disease a) COPD b) bronchiectasis c) cystic fibrosis d) alpha-1-antitrypsin deficiency e) prior pulmonary tuberculosis Epidemiology: 1) organism is ubiquitous in the environment 2) respiratory tract & GI tract are portals of entry 3) 18-44% of patients with AIDS will develop MAC without prophylaxis; 2% with effective antiviral therapy 4) white, middle-aged/elderly male smokers/COPD 5) non-smoking women over age 50 without underlying lung disease (Lady Windermere Syndrome) 6) most common nontuberculous mycobacterial infection [3] - most common cause of chronic lung infection worldwide [3] Pathology: 1) disseminated multiorgan infection - occurs in patients with HIV1 with CD4 counts < 50/uL & not received prophylaxis for MAC (see management) [3] 2) sustained bacteremia 3) generally late-stage HIV complication with CD4 < 50/mm3 4) localized disease syndrome (uncommon) a) hypersensitivity pneumonitis 'hot-tub lung' b) tuberculosis-like infection in elderly male smokers c) chronic right middle lobe syndrome, lingula infection & cough in elderly women (Lady Windermere syndrome) d) enteritis e) pericarditis f) osteomyelitis e) skin lesions g) soft tissue abscesses h) central nervous system lesions i) lymphadenitis [3] Clinical manifestations: 1) fever 2) night sweats 3) chronic cough 4) weight loss 5) fatigue 6) wasting 7) diarrhea 8) abdominal pain 9) hepatosplenomegaly 10) intra-abdominal lymphadenopathy 11) resembles tuberculosis symptomatically Laboratory: 1) complete blood count a) anemia (Hct < 30%) b) neutropenia 2) liver function tests - elevated alkaline phosphatase 3) sputum for acid-fast bacteria 4) sputum culture for Mycobacterium - repeat sputum culture if positive before treating - supposedly this will help distinguish infection for colonization (common) [3] 5) blood cultures 6) bone marrow biopsy & culture 7) antimicrobial sensitivities 8) Mycobacterium avium complex DNA 9) Mycobacterium avium complex rRNA 10) IFN-gamma release test is negative [3] Special laboratory: - bronchoalveolar lavage (BAL) Radiology: - resembles tuberculosis radiographically - nodular opacities with bronchiectasis in the right middle lobe on chest imaging (Lady Windermere syndrome) Complications: - immune reconstitution inflammatory syndrome occurs in AIDS patients with disseminated Mycobacterium avium complex [3] Management: 1) pulmonary disease or disseminated infection with patients with CD4 count < 50/uL sufficient to warrant therapy [3] a) organisms usually resistant to most conventional anti- mycobacterial agents* b) combination of 2 or 3 drugs 1] macrolide [3] a] clarithromycin 500 mg BID b] azithromycin 500 mg QD 2] ethambutol 25 mg/kg/day x 2 months, then 15 mg/kg/day + 3] with or without rifabutin 300 mg/day or rifampin 4] dosage 3 times weekly as effective as daily with fewer adverse effects [6] c) alternative agents 1] fluoroquinolone a] levofloxacin b] ciprofloxacin 500-750 mg BID 2] streptomycin 3] amikacin 10-15 mg/kg/day IV d) response may be expected after 2-8 weeks of therapy e) discontinue treatment after 12 months of successful treatment [4] 2) consider surgery for local or unresponsive disease 3) prophylaxis when CD4 count < 50/uL a) azithromycin 1200 mg weekly (prophylaxis of choice) b) clarithromycin 500 mg BID c) discontinue prophylaxis when CD4 count > 100/mm3 for 3 months [4] 4) empiric antibiotic therapy for Mycobacterial infection in a patients with advanced HIV infection a) isoniazid b) rifampin c) pyrazinamide d) ethambutol e) clarithromycin * Mycobacterium avium is frequently/generally resistant to isoniazid & rifampin.

Related

diagnosis of Mycobacterium avium intracellulare

Specific

Mycobacterium avium Mycobacterium avium paratuberculosis Mycobacterium intracellulare

General

Mycobacterium

Properties

KINGDOM: monera DIVISION: SCHIZOMYCETES

References

  1. Mayo Internal Medicine Board Review, 1998-99, Prakash UBS (ed) Lippincott-Raven, Philadelphia, 1998, pg 579
  2. Harrison's Principles of Internal Medicine, 13th ed. Isselbacher et al (eds), McGraw-Hill Inc. NY, 1994, pg 723
  3. Medical Knowledge Self Assessment Program (MKSAP) 11, 16, 17, 18, 19. American College of Physicians, Philadelphia 1998, 2012, 2015, 2018, 2021.
  4. Journal Watch 22(20):150, 2002 Yeni PG et al, JAMA 288:222, 2002 Dybul M et al, Ann Intern Med 137:381, 2002 MMWR Recomm Rep 51:1-64, 2002 http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5107a1.htm Masur H et al, Ann Intern Med 137:435, 2002 http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5108a1.htm
  5. Kasperbauer SH, Daley CL. Diagnosis and treatment of infections due to Mycobacterium avium complex. Semin Respir Crit Care Med. 2008 Oct;29(5):569-76 PMID: 18810690
  6. Jeong B-H et al. Intermittent antibiotic therapy for nodular bronchiectatic Mycobacterium avium complex lung disease. Am J Respir Crit Care Med 2015 Jan 1; 191:96. PMID: 25393520 - Bag R and Griffith DE. Therapy for Mycobacteriium avium complex lung disease. It ain't perfect, but it's progress. Am J Respir Crit Care Med 2015 Jan 1; 191:14 PMID: 25551346
  7. NEJM JWatch Question of the Week. March 27, 2018 https://knowledgeplus.nejm.org/question-of-week/562/
  8. Ebihara T, Sasaki H. Bronchiectasis with Mycobacterium avium Complex Infection. N Engl J Med 2002; 346:1372 PMID: 11986411 Free full text http://www.nejm.org/doi/full/10.1056/NEJMicm010899
  9. Kasperbauer SH, Daley CL. Diagnosis and treatment of infections due to Mycobacterium avium complex. Semin Respir Crit Care Med 2008 Sep 24; 29:569 PMID: 18810690