Phase 2 - Week 7 (MILE - Tuberculosis)

Question 1

Define tuberculosis

Answer 1

A bacterial infection caused by the bacterium Mycobacterium Tuberculosis. It results in the formation of ‘tubercules’ (granulomas), predominantly in the lungs.

Question 2

Describe the staining of M. Tuberculosis

Answer 2

• Cannot be classified as Gram positive or negative - stains as either
• Contains peptidoglycan in its cell wall
• Resistant to many stains but is called an acid-fast bacterium as once stained it resists decolorisation by acids

Question 3

Describe the structure of M. Tuberculosis and how this increases its virulence

Answer 3

• Typical bacteria structure - except cell wall which gives resistance
• Cell wall contains peptidoglycan and complex lipids composed of mycolic acids, cord factor and wax D
• Mycolic acids are strong hydrophobic alpha-branched lipids which form a lipid shell and prevent cationic proteins, lysosomes and oxygen radicals from phagocytic granules from attacking the mycobacterium
• High concentration of lipids in cell wall give resistance to antibiotic, acidic and alkaline chemicals, lysis by immune cells and phagocytosis
• Also gives ability to survive within macrophages

Question 4

How is tuberculosis most commonly contracted?

Answer 4

Via inhalation of airborne droplets containing the bacteria

Question 5

Describe the pathogenesis of primary tuberculosis

Answer 5

1. Bacteria inhaled
2. Bacteria inhabit alveoli
3. Bacteria ingested by alveolar macrophages and transported to lymph nodes where adaptive immune response is triggered
4. Body reacts to contain the infection within ‘tubercles’ or granulomas, which consist of epitheloid cells and giant cells
5. Tissue within granulomas becomes necrotic and caseous

Question 6

Describe the features of primary tuberculosis

Answer 6

• The presence of lesions and enlarged local lymph nodes indicates that primary tuberculosis has developed
• Can include bacillaemia and subsequent dessemination of infection to organs

Question 7

List the common sites for organ dissemination in tuberculosis

Answer 7

• Bone
• Adrenal glands
• Kidneys
• Brain

Question 8

What is the result of tuberculosis infection in organs?

Answer 8

Can lead to end-organ tuberculosis in which caeseous granulomatous destructive lesions form and can develop into a tumour-like mass of necrosis called tuberculomas.

Question 9

How does secondary tuberculosis occur?

Answer 9

• Bacilli may stay latent within macrophages in the lung apex for decades
• Can reactivate to cause secondary tuberculosis

Question 10

Describe secondary tuberculosis

Answer 10

• Necrotic tissue within the granulomas becomes liquified
• If granuloma is connected to an airway, debris will be coughed up, along with M. tuberculosis bacteria, allowing for further spread of disease
• This leaves a cavity in the lung, lined internally by granulomatous inflammation and externally by fibrotic tissue
• Lesion is called fibrocaeseous tuberculosis
• Can be spread of bacilli throughout the body to other organs during secondary tuberculosis, but to a lesser extent than primary tuberculosis

Question 11

List the risk factors associated with tuberculosis

Answer 11

• Being in close contact with a person who has infectious (secondary) tuberculosis
• Homelessness
• Intravenous drug use
• Being infected with HIV
• Diabetes mellitus
• Severe kidney disease
• Head and neck cancer
• Malnutrition
• Corticosteroid use
• Treatments for rheumatoid arthritis or Crohn’s disease

Question 12

Describe the symptoms of tuberculosis

Answer 12

Pulmonary symptoms:

• Cough lasting 3 weeks or longer
• Chest pain
• Haemoptysis
• Coughing up sputum

Other symptoms:

• Asthenia/fatigue
• Weight loss
• Loss of appetite
• Chills
• Fever
• Nocturnal hyperhidrosis

Latent tuberculosis is asymptomatic

Question 13

Describe the diagnosis of tuberculosis

Answer 13

• Presence of clinical symptoms
• Characteristic changes on a chest X-ray
• Mantoux test
• Stained smears of sputum, lung tissue or CSF used to identify acid-fast bacteria under a microscope
• Cultures of M. tuberculosis grown to confirm diagnosis
• Does not differentiate between latent and active tuberculosis - latent tuberculosis is diagnosed if patient has positive tuberculosis test but medical evaluation does not indicate tuberculosis disease

Question 14

Describe the characteristic changes seen on a chest X-ray in tuberculosis

Answer 14

• Consolidation of areas of the lungs
• Hilar enlargement due to lymphadenopathy
• Fibrotic scarring/calcification in healed primary or post-primary tuberculosis

Question 15

Describe a Mantoux test

Answer 15

• Purified protein derivative (tuberculin) is injected intradermally
• Result is interpreted 2-3 days later
• Induration of less than 6mm = negative result
• Induration of more than 6mm = positive result

Positive result means patient has had previous exposure to M. tuberculosis, not necessarily that the patient has tuberculosis.

Question 16

Describe how tuberculosis is treated in those with latent tuberculosis infection

Answer 16

• Often prescribed treatment to prevent development of the active form of the disease
• High risk groups in particular should be treated - e.g. HIV-infected, organ transplant recipients, intravenous drug users, children under 4 y/o
• Drugs used include - isoniazid, combined isoniazid and rifapentine and rifampin

Question 17

Describe the treatment of drug susceptible active tuberculosis

Answer 17

• Intensive phase of 2 months
• Continuation phase of 4 or 7 months (6-9 months in total)
• Intensive phase usually involves a combination of 4 drugs, which is reduced to 2 drugs in the continuation phase
• 7 month continuation phase only recommended for certain groups e.g. patients with HIV not receiving anti-retroviral treatment during their tuberculosis treatment

Question 18

Describe the treatment of drug-resistant tuberculosis

Answer 18

• Caused by tuberculosis bacteria which are resistant to at least one first-line anti-tuberculosis drug
• Multi-drug resistant tuberculosis is resistant to more than one anti-tuberculosis drug and at least isoniazid and rifampin (first-line drugs)
• Second-line drugs and other alternatives (e.g. fluoroquinolone) must be used instead, although they are less effective
• Patients with drug-resistant tuberculosis will be on a longer treatment plan (12-24 months)

Question 19

Describe the treatment of tuberculosis in patients infected with HIV

Answer 19

• In untreated latent tuberculosis + HIV, patients are much more likely to develop active tuberculosis
• Latent tuberculosis and HIV - daily dose of isoniazid for 9 months
• Active tuberculosis and HIV - intensive phase of isoniazid, rifmyacin, pyrazinamide and ethambutol for 2 months, continuation phase of isoniazid and rifmyacin for 4 months
• Interactions of anti-tuberculosis drugs and anti-retroviral drugs must be considered

Question 20

Describe the treatment of tuberculosis in pregnant women

Answer 20

• Infants born to women with untreated tuberculosis may have a low birthweight
• Latent tuberculosis and pregnancy - isoniazid daily or twice weekly for 9months with vitamin B6 supplementation
• Tuberculosis disease - isoniazid, rifampin and ethambutol daily for 2 months, then isoniazid and rifampin daily or twice weekly for 7 months
• Some drugs may have negative effect on foetus so should not be prescribed (e.g. streptomyocin)

Question 21

Describe the treatment of children with tuberculosis

Answer 21

• Once infected with M. tuberculosis, children are more likely to develop the active disease
• Latent tuberculosis treatment for children - isoniazid is most commonly used for 9 months
• Tuberculosis disease treatment for children - several anti-tuberculosis drugs for 6-9 months

Question 22

List the ways in which spread of infectious diseases is controlled

Answer 22

1. Immunisation
2. Screening
3. Compulsory treatment orders
4. Limiting contact with infectious patients
5. Control of antibiotic prescription

Question 23

Explain how immunisation is used to control the spread of infectious diseases

Answer 23

• Wide-spread immunisation leads to development of herd immunity
• Vulnerable members of the population who are unable to be vaccinated are protected by the immunisation of a high proportion of the rest of the population
• Therefore low chance of infection spreading

Question 24

Explain how screening can be used to control the spread of infectious diseases

Answer 24

Early screening of the population to identify individuals who are infected with or have been exposed to an infectious disease ensures early treatment and lower risk of further transmission

Question 25

Explain how compulsory treatment orders are used to control the spread of infectious dieases

Answer 25

• Normally patients have right to consent to medical treatment
• If they are unwilling/unable to consent and not being treated poses a significant risk of transmission of a serious infectious disease, public health authorities can authorise compulsory treatment
• E.g. due to problems with low compliance to tuberculosis treatment, directly observed therapy is often carried out to ensure patients are taking their medication

Question 26

Explain how limiting contact with infectious patients is used to control the spread of infectious diseases

Answer 26

• Isolating patients who have potentially been exposed to a serious infectious disease (quarantine) prevents transmission
• When a serious outbreak of disease occurs it can be hard to identify cases/carriers, so public spaces such as schools, cinemas etc. should be evacuated or closed

Question 27

Explain how control of antibiotic prescription can be used to control the spread of infectious diseases

Answer 27

In order to limit antibiotic resistance and transmission resistant strains of infections, the use of antibiotics should be carefully monitored