TB note 11 4

Spread

  • mostly from cough/airdrop
    • only 10 bacilli need to reach lung
  • very rarely genitourinary

Pathogenesis

  • phagocytosed by macrophage
  • antigen produce cellular instead of B cell response, CD 4 and 8
  • One of 2 outcomes
    • Latent: infection contained not eliminated. Granulomas
    • Active: not contained, spreads

Latent

  • asymptomatic and not contagious
  • 5% risk of reactivation first 1.5 years and then 5% risk lifetime reactivation

Active

  • Sx of fever, night sweats, weight loss caused by TNF alpha immune response
  • hemoptysis: cellular destruction and necrosis from immune response
  • Advanced HIV pts can have nl CXR
  • Other sx:
    • could be any organ sx or part of body
    • meningitis
    • hepatitis
    • spine, Pott's
    • lymph
    • pericardium

Latent TB Dx

  • Asymptomatic tests if:
    • from endemic and/or exposure
    • health care worker
    • immunocompromised condition, HIV
  • TB skin test
    • 5mm: HIV, organ transplant, immunocompromised
    • 15mm: no risks
  • Interferon gamma release assay: T cell response to TB ag in latent TB
    • NIL: negative control, patient's blood not with any antigens, < 8 iu/ml. If higher then underlying inflammatory condition that causes false positive
    • mitogen: positive control. Pt's blood with nonspecific activation of T cells, > 0.5. False negative can happen if < 0.5
    • TB-NIL: TB antigen minus negative control
    • Indeterminate: either negative or positive control failed. Test didn't work.

Active TB Dx

  • Do not order IGRA or skin test.
  • Sputum:
    • 3 AFB smears, 8 hours apart: immediately. Infectious if positive, but only noninfectious if negative. Can still have TB
      • non TB mycobacterium can stain positive
      • nocardia can stain positive
    • culture for M.TB
    • NAAT DNA probe, PCR: can also look for rifampin, INH resistance
  • CXR and CT
    • high sensitivity for active TB
    • low specificity 60-70%
    • HIV pt can have unremarkable CXR
  • Bronchoscopy:
    • bronc x1 has lower sensitivity than sputum x3
    • helpful if pt cannot produce sputum

Treatment

  • Prior to treatment
    • screen HIV
    • CXR Latent:
  • INH 9 months with B6
  • rifampin 4 months: can have more drug drug interactions
  • INH and rifapentin 3 months
  • Follow monthly
  • Ask about: nausea, anorexia, icterus, rash, paresthesia
  • monitor ALT, AST, T bili (inh rifampin cause hepatitis)
  • watchout out >3x upper limit of nl LFT

Active:

  • RIPE: 4 drugs 2 months, and then 4 months INH/rifampin
  • extend therapy if sputum clx positive after 2 months. Continue 7 months
  • extrapulmonary: 9-12 months

MDR TB

  • MDR if resistance to INH and rifampin
  • extensively drug resistance: INH, R, fluoroquinolone, aminoglycoside