Tuberculosis Flashcards
How many people worldwide are infected by TB?
2 billion
What is the relationship between HIV and TB?
Sufferers of TB and HIV will have much worse HIV symptoms as well as much worse TB symptoms
HIV patients also have an increased chance of contracting TB
Why is TB now a major problem in London, Manchester and Birmingham?
Due to immigration from high incidence areas; sub-Saharan Africa and South-east Asia
People of what social circumstance are most likely to be infected by TB?
People living in poverty, overcrowded conditions and malnutrition
What is the causative bacteria?
Mycobacteria
Where in the lungs is M. tuberculosis most likely to be found and why?
In the apices of the lung as it is aerobic and there it is high V and low Q
What are two mycobacteria that can cause TB?
Mycobacterium tuberculosis
M. bovis
What is the source of M. tuberculosis?
From coming contact with someone with a case of open pulmonary TB (coughing and sneezing)
What is the source of M. Bovis?
Through the consumption of infected cows’ milk (unpasteurised)
When droplets containing TB from a cough or sneeze are inhaled where must they land to cause an infection?
The alveoli
Describe how TB causes tissue damage?
- Macrophages in the alveolus phagocytose the bacteria
- They present antigens from the bacteria to Th cells in the lymph nodes
- Th1 cells specific to the antigen move back to the alveoli and bind to macrophages
- This induces the macrophages to become activated
- Activated macrophages become epithelioid cells
- Fusion of epithelioid cell forms Langhan’s giant cell
- Accumulation of all three cells -> granuloma
- Central caveating necrosis (may later calcify)
What is the pro and con of the Th1 cell mediated immunological response?
Reduces number of invading particles
BUT
Causes tissue destruction as a result of activation of macrophages
What are the two types of host?
Resistant and susceptible
What happens if Mycobacteria infects a susceptible host?
Lots of tissue destruction
Organism proliferates
Progressive disease
What happens if Mycobacteria infects a resistant host?
Minimal or no tissue destruction
Organism contained
Little or no disease
How does the infection spread throughout body?
Spreads via lymphatic to draining hilar lymph nodes, then enters blood and spreads to all organs of body
What are the symptoms of TB?
Usually none Can be: Fever Malaise Erthema nodosum
What are the 3 possible outcomes of primary infection in TB?
Cleared - get rid of infection and develop immunity
Latent - remains in granulomas
Progressive disease
What occurs if the primary infection progress?
Cavitation in initial area of infection
Enlarged hilar lymph compresses bronchi and cause lobar collapse
Enlarged lymph node discharged into bronchus -> tuberculous Bronchopneumonia
What two causes of post primary disease?
- Reactivation of mycobacterium from latent primary infection
- Re-infection: either have immunity or could have insufficient immunity leading to progression
What can occur 6-12 months after primary infection?
Milary TB - mottling on X-ray
Meningeal TB - CSF high protein
TB pleural effusion
What are symptoms of a post-primary pulmonary TB?
May be none, but is slowly progressive Cough Sputum Haemoptysis Pleuritic chest pain SOB Sytemically unwell: malaise, fever, weight loss
What do you look for in the PMH if suspect post-primary TB?
Diabetes
Immunosuppressive disease
Previous TB
What do you look for in the drugs history if suspect post-primary TB?
Immunosuppressive drugs
What do you look for in the PSH if suspect post-primary TB?
Alcohol
IVDA
Poor social circumstance
Immigrants from high incidence areas
What are the sign of post-primary TB?
May be none If more advanced: Crackles Bronchial breathing Finger clubbing (rare unless severe)
What are risk factors for TB?
Immunosuppressed (HIV, ICS) Malnourished Alcoholism Diabetes M Adolescence, elder Recent immigrant from high prevalence countries
How is the diagnosis made?
By finding the organism - sputum culture
What are essential investigations?
3 sputum specimens on successive days:
Sputum smear
Sputum culture
CXR
What can a CXR show to indicate TB?
Patchy shadowing (often in apices)
Cavitation
Calcification (if chronic or healed TB)
What investigations do you carry if sputum is negative but still suspicious?
CT thorax
Bronchoscopy and trans bronchial biopsy (to culture organisms)
Pleural aspiration and biopsy if pleural effusion (for fluid cytology)
What are the rule for treatment of TB?
Multiple drug therapy to prevent resistance for at least 6 months
Specialist only
Doctor required legally to notify all cases to public health
What drugs are given for the first two months?
Rifampicin
Isoniazid
Ethambutol
Pyrazinamide
What drugs are then given for 4 months?
Rifampicin
Isoniazis
After hoe long after treatment is TB rendered a non-infectious disease?
Two weeks
What are side effects of rifampicin?
Orange tears and ruin
Induces liver enzyme
Oral contraceptive ineffective
Heptitis
What are side effects of isoniazid?
Hepatitis
Peripheral neuropathy
What are the side effects of ethambutol?
Optic neuropathy
What is the side effect of pyrazinamide?
Gout
Why is TB contact tracing important?
Identify source
Identify transmission
What does the likelihood of infection depend on?
Duration of contact
Intensity of infection
What are the general actions of TB contact tracing?
First screen close household contact
If close contact infected, then screen casual contacts
What screening tests are given to people < 16yrs and NO BCG vaccine
Tuberculin test (Head or Mantoux) Should be tuberculin negative
Explain the tuberculin test and how it is interpreted
Tuberculin gets injected which contains inactive TB bacteria
Positive result: in latent TB infection, a hard red bump will develops at injection site
Negative result: Skin won’t react, might take long to develop so retest later
What investigations are carried out in < 16yrs and NO BCG, if the heaf positive meaning TB exposure?
CXR
Normal: chemoprophylaxis rif and inh 3 months, then inh for 6 months
Abnormal: Primary TB and treat
What screening test is done for > 16yrs and BCG vaccine?
CXR
Normal: discharge
Abnormal: investigate for TB and treat if necessary
