Tuberculosis

Question 1

Which bacteria causes tuberculosis?

Answer 1

Mycobacterium tuberculosis

Question 2

Mycobacterium tuberculosis:

• Shape
• Size
• Doubling time

Answer 2

• Rod shaped
• 2-5 micrometers by 0.2-0.5 micrometers
• Slow growing doubling time ~18 hours

Question 3

How is tuberculosis spread?

Answer 3

Mode of transmission is via aerosol route (coughing, sneezing, spitting)

Question 4

Which type of necrosis is associated with tuberculosis?

Answer 4

Caseous necrosis

Question 5

Systemic features of tuberculosis

Answer 5

Low grade fever, anorexia, weight loss, malaise, night sweats, clubbing, erythema nodosum

Question 6

Presentation of pulmonary tuberculosis

Answer 6

Cough (in ~50% >3 weeks, dry then productive), pleurisy, pleural effusion, haemoptysis (not common)

Question 7

Least to most effective immune response in tuberculosis

Answer 7

Miliary → meningeal → pulmonary (widespread) → pulmonary (localised) → localised extra pulmonary → lymph node → healthy contact (latent TB infection)

Question 8

Diagnosis of active TB

Answer 8

History and examination, simple blood tests, radiology/imaging, microbiology and histology

Question 9

Some findings on a CXR of active TB

Answer 9

• Fibronodular/linear opacities
• Cavitation
• Calcification
• Miliary disease
• Effusion
• Lymphadenopathy

Question 10

Which specimens are needed for microbiological testing?

Answer 10

• Sputum x3, gastric washings, bronchoalveolar lavage
• Early morning urines x3
• Biopsies

Question 11

What microbiological test is quickest in diagnosing TB

Answer 11

Nucleic acid amplification test (<8 hours diagnosis)

Question 12

Diagnosis of latent TB

Answer 12

• Should be offered to close contacts of those with TB, immune dysfunction, healthcare workers and high risk populations
• Tuberculin skin testing or interferon gamma release assays

Question 13

Tuberculin skin testing

Answer 13

Intradermal injection of protein derivative tuberculin. Suggestive of TB if size of skin induration >5mm if risk factors, >15mm no risk factors

Question 14

Procedures performed on specimens to help diagnose tuberculosis

Answer 14

Microscopy (Ziehl-Neelsen, Auramine), culture (solid phase, liquid phase, drug sensitivities), histology (granulomata with central caseous necrosis)

Question 15

Treatment of drug sensitive tuberculosis - active

Answer 15

4 drugs for 2 months: rifampicin, isoniazid, pyrazinamide, ethambutol
2 drugs for further 4 months: rifampicin and isoniazid

Question 16

Treatment for drug sensitive tuberculosis - latent

Answer 16

2 drugs for 3 months: rifampicin and isoniazid
or
1 drug for 6 months: isoniazid

Question 17

Immune response to tuberculosis

Answer 17

Step 1: Phagocytosis
Step 2: Immune recognition and innate effector mechanisms
Step 3: Slow onset of Th1-biased adaptive immunity (key to anti-TB immune responses

Question 18

Which cell is the initial intracellular primary niche of M.tuberculosis

Answer 18

Macrophage

Question 19

Active tuberculosis infection:

• When does it occur?
• What can it arise from?

Answer 19

• When containment by immune cells (T cells and macrophages) is inadequate
• Can rise from primary infection or re-activation of previously latent disease

Question 20

Latent tuberculosis infection without disease:

• What does this mean?
• What is it due to?

Answer 20

• There is a positive skin/blood test showing evidence of infection but the patient is asymptomatic and non-infectious
• Due to persistent immune system containment (granuloma formation prevents bacterial growth and spread)

Question 21

Risk factors for reactivation of latent tuberculosis

Answer 21

• New infection
• HIV
• Organ transplantation
• Immunosuppression
• Silicosis
• Illicit drug use
• Low socioeconomic factors
• High risk settings
• Haemodialysis