Tuberculosis

History

• Died from or infected by Tb
  • John Keats (poet)
  • George O'well
  • Nelson Mandella

• Hippocrates description
  • Phthisis (to waste away, consumption)

• Robert Koch found the bacteria 1882

Epidemiology

est. case est. death all form 10mil 1.4mil HIV-ass 0.9 mil 208,000 MDR-Tb ≈558,000 ≈190,000

• 8 countries account for 2/3 of all worldwide Tb

1. India
2. China
3. Indonesia
4. the Phillippines
5. Pakistan
6. Nigeria
7. Bangladesh
8. South Africa

Transmission

• transmission-influencing factors
  • sputum status of index case
  • proximity - distance between each other
  • time
• susceptibility of person

• [math]\displaystyle{ R_0 \approx r \times c \times d }[/math]
  • [math]\displaystyle{ r }[/math] = transmissibility
    • to reduce [math]\displaystyle{ r }[/math]
      • ealier detection
      • rapid commencing of treatment
      • reduce aerolization (surgical masks on patients)
        • surgical masks on patients reduce infectivity by 56%
  • [math]\displaystyle{ c }[/math] = susceptibility of contacts
    • to reduce [math]\displaystyle{ c }[/math]
      • open windows
        • Tb airborne transmission risk: windows closed 97%, negative pressure room (ACH12) 39%, windows and doors fully open 33%
      • N95 respirator
      • ARTs for HIV patients
  • [math]\displaystyle{ d }[/math] = duration of infectivity
    • to reduce [math]\displaystyle{ d }[/math]
      • treat patients appropriately

Risk factors

• HIV
• malnutrition
  • Tb risk inversely correlates with BMI
• diabetes
  • diabetes and Tb are syndemic
  • diabetes and Tb pathophysiologically exacerbate each other even under treatment condition in terms of hepatotoxicity
• overcrowding
  • people per room vs Tb rate per 100,000 (in Canada)
    • 0.4-0.6 vs 18.9
    • 1.0-1.2 vs 113
• ....

Natural history

1. inhalation of M.tb containing droplets
2. macrophages phagocytosis
3. granuloma + lymphadenopathy
4. Ghon complex - primary infection
   1. 5% local progression/disseminated Tb
   2. 95% latent Tb
      1. 10% of latent Tb reactivates in lifetime - secondary Tb

Latent Tb

• 1/3 of the world's population have latent Tb
  • modelling approx. 1.7 bil. people
• 10% of those latent Tb people get reactivation in their lifetime

Symptoms

• cough ± sputum ± hemoptysis > 2weeks
• fever
• malaise
• weight loss

• pulmonary
  • 80-85% of TB diagnosis are pulmonary
• extra-pulmonary
  • lymphadenitis - hilar/other
    • cold abscess
    • more common in cervical and hilar
    • possibly in axillar, inguinal and abdominal
    • hilar adenitis DDx - sarcoidosis, lymphoma, histoplasmosis
  • pleural
    • usually uni-lateral
    • effusion high LDH, high protein, high lymphocyte
  • intestinal
    • can mimic Crohn's disease
    • most common in ileocecal
  • meningitis
    • often involves 3rd and 6th cranial nerves
    • meningeal irritation signs often unaccompanied
  • cerebral tuberculoma
    • DDx primary CNS lymphoma
  • Pott's disease (vertebral destruction due to TB)
    • kyphosis, gibbus formation
    • sometimes extends to psoas muscle abscess;
  • arthritis
    • synovial fluid does not necessarily contains enough TB bacteria; fluid culture may miss diagnosis
    • IGRA could be clue
  • ......

• miliary TB
  • massive lymphohematogenous dissemination
    • nodules diameter <10mm
  • liver
  • spleen
  • bone marrow
  • lungs
    • pulmonary miliary TB easily missed by chest X-ray
  • meninges