TB Flashcards
What is TB caused by?
-Tuberculosis (TB) is an infectious disease caused by the mycobacterium tuberculosis bacteria. It is a small rod shaped bacteria (a bacillus).
-the TB bacteria are described as acid-fast bacilli. They require a special staining technique using the Zeihl-Neelsen stain. This turns TB bacteria bright red against a blue background.
How is the disease caused?
It is mostly spread by inhaling saliva droplets from infected people. It then spreads through the lymphatics and blood. Granulomas containing the bacteria form around the body.
Active TB is where there is active infection in various areas within the body.
When latent TB reactivates this is known as secondary TB. When the immune system is unable to control the disease this causes a disseminated, severe disease and is referred to as miliary TB.
Where can extrapulmonary TB occur?
Lymph nodes. A “cold abscess” is a firm painless abscess caused by TB, usually in the neck. They do not have the inflammation, redness and pain you would expect from an acutely infected abscess.
Pleura
Central nervous system
Pericardium
Gastrointestinal system
Genitourinary system
Bones and joints
Cutaneous TB affecting the skin
Risk Factors
Known contact with active TB
Immigrants from areas of high TB prevalence
People with relatives or close contacts from countries with a high rate of TB
Immunosuppression due to conditions like HIV or immunosuppressant medications
Homeless people, drug users or alcoholics
How does the BCG vaccine work?
The BCG vaccine involves an intradermal infection of live attenuated (weakened) TB. It offers protection against severe and complicated TB but is less effective at protecting against pulmonary TB.
Prior to the vaccine patients are tested with the Mantoux test and given the vaccine only if this test is negative. They are also assessed for the possibility of immunosuppression and HIV due to the risks related to a live vaccine.
BCG vaccine is offered to patients that are at higher risk of contact with TB:
Neonates born in areas of the UK with high rates of TB
Neonates with relatives from countries with a high rate of TB
Neonates with a family history of TB
Unvaccinated older children and young adults (< 35) who have close contact with TB
Unvaccinated children or young adults that recently arrived from a country with a high rate of TB
Healthcare workers
Presentation
Lethargy
Fever or night sweats
Weight loss
Cough with or without haemoptysis
Lymphadenopathy
Erythema nodosum
Spinal pain in spinal TB (also known as Pott’s disease of the spine)
Mantoux test (investigation)
The Mantoux test is used to look for a previous immune response to TB. This indicates possible previous vaccination, latent or active TB.
This involves injecting tuberculin into the intradermal space on the forearm. Tuberculin is a collection of tuberculosis proteins that have been isolated from the bacteria. The infection does not contain any live bacteria.
Injecting the tuberculin creates a bleb under the skin. After 72 hours the test is “read”. This involves measuring the induration of the skin at the site of the injection. NICE suggest considering an induration of 5mm or more a positive result. After a positive result they should be assessed for active disease.
Interferon-Gamma Release Assays (IGRAs) investigation.
his test involves taking a sample of blood and mixing it with antigens from the TB bacteria. In a person that has had previous contact with TB the white blood cells have become sensitised to those antigens and they will release interferon-gamma as part of an immune response. If interferon-gamma is released from the white blood cells then this is considered a positive result.
The IGRA test is used in patients that do not have features of active TB but do have a positive Mantoux test to confirm a diagnosis of latent TB.
X ray (investigation)
-Primary TB may show patchy consolidation, pleural effusions and hilar lymphadenopathy
-Reactivated TB may show patchy or nodular consolidation with cavitation (gas filled spaces in the lungs) typically in the upper zones
-Disseminated Miliary TB give a picture of “millet seeds” uniformly distributed throughout the lung fields
Which cultures should you collect?
-Sputum. 3 samples should be collected and tested. If they are not producing sputum then hypertonic saline can be used to induce sputum that can be collected.
-They might require bronchoscopy with lavage to collect sputum samples.
-Mycobacterium blood cultures. These require special blood culture bottle.
-Lymph node aspiration or biopsy
-Nucleic acid amplification testing is a way of looking for the DNA of the TB bacteria. It is tested on a sample containing the bacteria (i.e. sputum sample). It provides information about the bacteria faster than a traditional culture but is only used where having this information would affect treatment or they are at higher risk of developing complications e.g HIV
Management of Latent TB
Otherwise healthy patients do not necessarily need treatment for latent TB. Patients at risk of reactivation of latent TB can be treated with either:
Isoniazid and rifampicin for 3 months
Isoniazid for 6 months
Management of Acute Pulmonary TB
Management of active TB is coordinated by a specialist TB service with an MDT approach.
RIPE is the mnemonic used to remember the treatment for TB. It involves a combination of 4 drugs used at the same time:
R – Rifampicin for 6 months
I – Isoniazid for 6 months
P – Pyrazinamide for 2 months
E – Ethambutol for 2 months
Other Management Considerations
Test for other infectious diseases (HIV, hepatitis B and hepatitis C).
Test contacts for TB.
Notify Public Health of all suspected cases.
Patients with active TB should be isolated to prevent spread until they are established on treatment (usually 2 weeks). In hospital negative pressure rooms are used to prevent airborne spread.
Management and followup should be guided by a specialist MDT.
Treatment is slightly different for extrapulmonary disease and often includes using corticosteroids.
Individualised drug regimes are required for multidrug‑resistant TB.
Side Effects of Treatment
Rifampicin can cause red/orange discolouration of secretions like urine and tears. It is a potent inducer of cytochrome P450 enzymes therefore reduces the effect of drugs metabolised by this system. This is important for medications such as the contraceptive pill.
Isoniazid can cause peripheral neuropathy. Pyridoxine (vitamin B6) is usually co-prescribed prophylactically to reduce the risk of peripheral neuropathy.
Pyrazinamide can cause hyperuricaemia (high uric acid levels) resulting in gout.
Ethambutol can cause colour blindness and reduced visual acuity.
Rifampicin, isoniazid and pyrazinamide are all associated with hepatotoxicity
