Respiratory TB and Pneumonia: 53-109 Flashcards
What is the microbiology of mycobacterium tuberculosis?
Non-motile rod shaped bacteria
Obligate aerobe
Long chain fatty acids, complex waxes and glycolipids in cell wall
Slow growth compared to others
Where are the regions affected by extra-pulmonary TB?
- Lymphadenitis (Scrofula, Cervical lymph nodes most commonly, Abscesses and sinuses)
- Gastrointestinal (Swallowing of tubercles)
- Peritoneal (Ascitis or adhesive)
- Genitourinary (Slow progression to renal disease, Subsequent spreading to lower urinary tract)
- Bone and joint (Haemotgenous spread, Spinal TB is most common, Potts disease)
- Tuberculous meningitis (Chronic headache, fevers, CSF – markedly raised proteins, lymphocytosis)
What is military TB?
Bacilli is spread through the blood stream
- Headaches suggest meningeal involvement
- Pericardial, pleural effusions small
- Ascites may be present
- Retinal involvement (choroid tubercles seen)
What is the transmission of TB?
- Spread by respiratory droplets –coughing, sneezing
- Droplet nuclei
- Suspended in air
- Reach lower airway
How easy is it to catch TB?
Contagious but not easy to acquire infection. Prolonged exposure to active TB individuals facilitates transmission
What is the pathogenesis of TB?
- Engulfed by alveolar macrophages
- Unique structure allows the TB bacteria to evade destruction by macrophages. Can survive and multiply within the macrophage
- TB bacilli from the macrophage can get carried to the lymph nodes during drainage
- Formation Primary complex (Ghon’s focus + draining lymph nodes)
- Minority (5%) – Can proceed to active disease after the primary complex. Primary TB develops
- Majority of patient – latent infection (95%). Containment of the infection to prevent the bacilli from multiplying. Live organism in the site of infection and lymph node
- Small number of latent infection patient can develop post primary. 2 years after the initial infection.
What is the effect of post primary TB?
Reactivation and hypersensitivity can occur. Massive destruction of the lung due to increased inflammatory response and bacterial damage. This can also occur with reexposure to the bacteria
What determine the formation of the primary complex?
- The infectious dose
- Strain of TB
- Immune response to the TB bacilli which depends on T cells to decide fate of primary complex (HIV)
Compare Latent Tb and Active TB.
Latent TB
- Inactive, contained tubercle bacilli in the body
- TST or IFN gamma test results usually positive.differentiate
- Chest X-ray usually normal
- Sputum smears and cultures negative
- No symptoms
- Not infectious
- Not a case of TB
Active TB
- Active, multiplying tubercle bacilli in the body
- TST or blood test results usually positive
- Chest X-ray usually abnormal
- Sputum smears and cultures may be positive
- Symptoms such as cough, fever, weight loss
- Often infectious before treatment
- A case of TB
Why doesn’t the TST or IFN test differentiate between latent and active TB?
Both Latent and Active have Primary Complex so doesn’t differentiate between the two.
What are the histological features of Tuberculosis?
-Caseating granuloma is lung parenchyma and/or mediastinal lymph nodes
Where are the features of TB on an X-ray?
- Apex of the lung often involved
- Ill-defined paths consolidation
- Cavitatons usually develop with consolidation
- Healing results in fibrosis
How is a TB diagnosis established through investigations?
- Culture is the Gold standard technique
- NAAT
- Chromatography
How are antibiotics tested for effect on a micro-organism?
Drug sensitivity test
What are symptoms of TB?
- Night sweats
- Tiredness and malaise
- Weight loss and anorexia
- Fever
- Cough
- Haemoptysis occasionally
- Breathlessness if pleural effusion
What are the signs seen on examination for TB?
- Often no chest signs despite CXR abnormality
- Maybe crackles in affected area
In extensive disease
- Sings of cavitation
- Fibrosis
-Pleural involvement: typical signs of effusion
What is important about the history of a TB patient?
- Ethnicity
- Recent arrival or travel to high TB burden countries
- Contacts with TB
- BCG vaccination
- Specific clinical features
- Fever
- Weight loss
- Malaise
- Anorexia
What are the risk factors of TB?
- Non-UK born/recent migrants (South Asia, Sub-Saharan Africa)
- HIV – latent infections can reactivate due to the immune system being affected
- People sustpected of TB are tested for HIV
- Other immunocompromised states
- Homeless
- Drug users, prison
- Close contacts
- Young adults
How are People suspected of TB managed?
- Early and adequate treatment
- Close monitoring of compliance to treatment (Direct observed therapy, Video observed therapy)
- Treatment for a long duration due to long duration of TB to multiply
What is the First line medication to treat TB?
- Rifampicin (orange pee)
- Isoniazid
- Pyrazinamide
- Ethambutol
2nd line
Quinolones
