TB stats
- No. 1 communicable disease, causes more death than HIV + malaria combined
- 2 times more common in women
- 2 billion people infected world-wide
- 15 times more likely to get TB if non-UK born
which 8 countries have 2/3 of TB cases?
India, China, Indonesia, Philippines, Nigeria, Bangladesh, South Africa
vulnerable groups for TB
- elderly, neonates
- immunocompromised, HIV
- from high-prevalent countries
- age 15-44
- diabetic
- underlying nutritional state
3 TB - causing organisms
- M. tuberculosis
- M. africanum
- M. bovis
non TB organisms
- atypical mycobacteria infections
- M. leprea
describe MTB (mycobacterium tuberculosis)
- slow growing (therefore takes a long time before strain and treatment is determined)
- thick walled (resistant to macrophages, neutrophils, acids, alkalines, detergent, alcohol)
- non-motile
- require long treatment courses
- aerobic (therefore TB is mostly found at the apices of the lungs where there V>Q and there is less gas exchange)
transmission of TB
- airborne
- only pulmonary and laryngeal TB communicable, but TB can affect may organs
- requires prolonged exposure
progression of inflammatory response in TB
activated macrophages –>
- –> cytokine response –> T cells (kills the pathogens)
- –> epitheloid cells –> Languan’s giant cells –> granuloma formation
what type of infection is TB?
IL-6 mediated pyogenic infection
3 possible outcomes of primary TB infection
- progressive disease
- contained latent
- cleared and cured (lung can heal with or without scar)
describe primary TB infection and its common presentations
- no preceding exposure
- MTB spread through the lymphatics to the draining hilar lymph nodes
- usually no symptoms aside from: fever, malaise, possible chest signs
- erythema nodosum
- Gohn focus (past TB)
complications of primary TB infection
- severe bronchial pneumonia (1%)
- miliary TB (1-3%)
describe severe bronchial pneumonia as complication of TB
- cavitation: the primary focus continues to enlarge
- enlarged hilar lymph node compresses the bronchi –> lobar collapse
- enlarged lymph node discharges into the bronchus
describe miliary TB
- shows as millet seeds in autopsy
- caused by spread of TB from blood to lungs
- in 10-30%, there is haematogenous spread (by blood) to CNS TB, the rest to other organs
describe post primary TB and 2 reasons why it can go unnoticed
- the kind of TB that we see the most.
- only in humans, animals die from primary TB
- take decades to develop, therefore the person probs have TB from childhood.
- 85% of cases will heal on its own
why it goes unnoticed until now:
- MTB enters latent stage and does not proliferate
- there is equal proliferation of MTB and destruction by immune cells
timeline for TB disease progression
primary complex –> progressive primary disease –> miliary TB, meningeal TB, pleural TB (after 6-12 months) –> post primary disease (pulmonaryTB, skeletal TB ) (after 1-5 years) –> genitourinary TB, cutaneous TB (after 10-15 years)
TB presentation
- fever (absent in 37%)
- weightloss (absent in 38%)
- night sweats (absent in 39%)
- all 3 absent in 25%
- cough (only in pulmonaryTB - about half of all TB)
- fluffy nodular upper zone cavitation in 10-30%
- CRP (normal in 15%)
- ESR (erthrocyte sedimentation rate) - normal in 21%
investigations for TB:
- CXR (sometimes will show as normal)
- CT
- lymphadenopathy
- CRP
- ESR
- BAL
- sputum samples (8-24 hours apart, one morning sample)
- lumbar puncture in CNS TB
- urine test in urogenital TB
- biopsy, tissue sample
- Manoux or IGRA
when to consider C scan for TB
- normal CXR but suspect miliary TB
- cavitation or other differential
- lymphadenopathy present (enlarged lymph nodes)
- when planning to conduct bronchoalveolar lavage/washing (BAL)
alternative diagnosis for TB
- granulomas/ giant cells present
- lymphadenopathy (pneumonia does not have this, but some other conditions do, make sure to eliminate those first) - usually unilateral, 15% bilateral
describe BAL
bronchoscope passed into the lungs through nose/mouth. Water is squirted into a part of the lungs and collected for analysis
5 drugs for TB and the year they were discovered
- streptomycin - 1944 (not used anymore, resistance)
- isoniazide (H) - 1952
- pyrazinamide (Z) - 1952
- rifampicin (R) - 1957
- ethambutol (E) - 1961
standard treatment plan for TB
2 months of 4 drugs (R/H/Z/E) + 4 months of 2 drugs (R/H)
total of 6 months, around 12 tablets per day
alternate TB treatment plans
- 7-9 months monoresistance treatment (single-agent?)
- 12 months (for CNS TB, H monoresistance extensive disease)
- 9-12-18-20 months (MDR-RR TB)
