Tuberculosis Flashcards
What is TB
An infection caused by Mycobacterium tuberculosis that may affect any part of the body but most commonly affects the lungs
How is TB spread
By a person inhaling the bacterium in droplets coughed or exhaled by someone with infectious TB
How many people have the active disease
15-20 million
How many people have the latent disease
2 billion
What ethnic groups is TB highest in
Black African
Pakistani
Indian
What has caused the recent increase in notification rates
The patterns of immigration and increasing international travel
What other groups of people have a high incidence of TB
Alcoholics, homeless, those misusing drugs, those coinfected with HIV
What type of TB do young people get
Newly acquired TB
What type of TB do older age groups get
Reactivation of latent infection
What are the two main patterns of the disease
Primary and post-primary
What is primary tuberculosis
The pattern of disease seen with first infection in a person (often a child) without specific immunity to TB
How is primary tuberculosis acquired?
By inhalation of organisms from an infected individual
What appears on the CXR in primary tuberculosis
Ghon focus ( a peripheral area of consolidation)
What does healed primary focus appear as on a CXR
Calcified nodules
Bronchiectasis in which lobe is a very typical outcome of hilar node involvement by TB in childhood
Middle
What might haematogenous spread of infection result in
Early generalisation of disease that may cause miliary TB and the lethal complication of tuberculosis meningitis
Describe post-primary TB
The pattern of disease seen after the development of specific immunity
When would post-primary TB typically occur
Following direct progression of the initial infection or result from endogenous reactivation of infection or from exogenous reinfection in a patient who has had previous contact with the orgnaism and has developed a degree of specific immunity
Where is the most common pulmonary site of infection for post-primary TB
The apices of the lungs
What are the most typical chest symptoms of TB
Persistent cough, sputum production and haemoptysis
What are the most typical systemic symptoms of TB
Fever, night sweats, anorexia and weight loss
What is the most common appearance of TB on a chest xray
Cavitating apical lesions
How should sputum samples be examined in the lab
By the Ziehl-Neelsen method looking for AAFB that appear as red rods on a blue background
What is the disadvantage of using the Ziehl-Neelsen method
It takes a long time for the laboratory tests to come back
What is the current standard treatment of TB
6 months of rifampicin and isoniazid supplemented by purazinamide and ethambutol for the first 2 months
Why is rifampicin and isoniazid used for so long?
To eradicate bacilli that may be lying dormant
What should be instituted for patients who have difficulty complying with TB treatment
Directly observed therapy - observed to ensure that he or she swallows the medication
How is directly observed therapy sometimes achieved
By giving high doses of the anti-TB medication three times per week with the patient attending a hospital or GP clinic to be given the medication under the supervision of a doctor or a nurse
What are the adverse effects of isoniazid
Hepatitis, neuropathy
What are the adverse effects of Rifampicin
Hepatitis, rashes, enzyme induction
What are the adverse effects of pyrazinamide
Hepatitis and rashes and elevated uric acid
What are the adverse effects of ethambutol
Optic neuritis
What are the adverse effects of ethambutol
Optic neuritis
What should be checked before commencing ethambutol
Visual acuity
What is latent TB
The situation where a person has been infected with Mycobacterium tuberculosis at some time but does not currently have the active disease
What are the factors that increase the risk of reactivation of TB
Aging Alcohol misuse poor nutrition coinfection with HIV use of immunosuppressive drugs
How is detection of latent infection carried out
Demonstrating an immune response to Mycobacterium tuberculosis using a tubercilin test or an interferon gamma based blood test
What type of hypersensitivity response occurs during the tuberculin testing and what can be seen
Type 4 cell mediated - results in a raised area of induration and reddening of the skin
How is the tuberculin solution injected in the Mantoux test
Intradermally
What indicates a positive result to the Mantoux test
Redness and induration at least 10mm in diameter
How is the Heaf test performed
With a spring loaded needled “gun”
How is the reaction of the Heaf test graded
From 1- 4 according to the formation of papules and the extent of induration
What does a negative tuberculin test indicate
BCG is recommended as it makes active TB unlikely and therefore there would be a lack of immunity
What is the most useful and more specific diagnosis of a latent TB infection
Interferon Gamma blood tests but they should not be used as a routine diagnostic tool for active TB
How long are sputum positive patients infectious for
Until they have completed 2 weeks of treatment
What does screening of contacts consist of
Checking for symtpoms
Chest Xray
tuberculin testing
interferon-gamma test and assessment of BCG status
What reduces the risk of future activation of the latent disease
Chemoprophylaxis
What does chemoprophylaxis consist of?
6 months with isoniazid alone or for 3 months with isoniazid and rifampicin
Why are only 1 or 2 drugs used in the treatment of latent TB and 4 in active TB
there are a thousand times fewer bacteria than in active TB
Describe the screening process of immigrants for TB
For immigrants from areas with a high prevalence of TB (africa, indian subcontinent ) should be screened for TB on arrival in a country of low prevalence sucha s the UK
Adults have CXR and children have a tuberculin test.
What is the BCG vaccination
A live attenuated strain of TB that provides about 75% protection against TB for about 15 years
How is the BCG vaccination given
Intradermal injection
