TB

Question 1

What stain is used to identify TB?

Answer 1

Ziehl-Neelson stain

Pink/red slender TB bacilli

Question 2

Describe the cell wall of TB

Answer 2

Contains peptidoglycan and complex lipids

But will not gram stain

Question 3

Why can a gram stain not be used to identify TB?

Answer 3

Waxy coating on cell surface makes cell impervious to gram staining

Question 4

What MO causes TB?

Answer 4

Mycobacterium tuberculosis

Question 5

What are the most prevalent species of TB?

Answer 5

M tuberculosis
M bovis
M africanum

Question 6

Discuss the transmission of TB

Answer 6

By respiratory droplets = coughing, sneezing

Infectious dose = 1-10 bacilli

Question 7

In what setting is TB most likely to spread?

Answer 7

Close proximity institutions = prisons, dense living conditions

Question 8

Outline the pathogenesis of TB

Answer 8

1) inhaled infectious droplets
2) engulfed by macrophages
3) local lymph nodes
4) forms primary complex = ghons focus + draining LN (5% progress to primary disease, tissue damage)
5) initial containment of infection
6) latent infection

Then either 1) reactivation, post primary TB, 2) cures (95%)

Question 9

What is the most important immune response against TB, and why?

Answer 9

Cellular response (T cells)as Tb has infected the macrophages = intracellular

Question 10

Who is very at risk of TB?

Answer 10

HIV pts = don’t have the immune response to control the infection

Question 11

How can TB be divided?

Answer 11

Primary
Post-primary
Latent

Question 12

Discuss the characteristics latent TB

Answer 12

Inactive, contained tubercle bacilli in body

TST/IFN +ve

Chest x-ray normal

Sputum smears/cultures -ve

No symptoms
Not infections

Question 13

Discuss the characteristics of TB disease

Answer 13

Active multiplying tubercle bacilli

+ve TST

Abnormal CXR

Sputum smear/cultures +ve

Symptoms = cough, fever, weight loss

Question 14

What is TST?

Answer 14

Tuberculosis sensitivity test

Mantoux

Screening for TB

Intradermal TB Ag injection

False +ve = BCG, non TB

Question 15

What is an IFN test?

Answer 15

Detection of Ag specific IFN-gamma prod

Cannot distinguish latent and active TB

Question 16

What is a ghon focus/complex?

Answer 16

Lesion in the lung consisting of calcified focus of infection and an associated LN

Question 17

What is post-primary TB?

Answer 17

Reactivation Or exogenous re-infection

Question 18

What are the risk factors for the reactivation of TB

Answer 18

Infection with HIV

Substance abuse

Prolonged therapy with corticosteroids

Immunosuppressive therapy

TNF-alpha antagonists

Organ transplant

DM

Question 19

On histology what is the typical appearance of TB?

Answer 19

Caseating granuloma

Lymphocytes fused to form giant cells

Inflam cells

Caseous necrosis centre

Question 20

What sites of the body can become effected by TB?

Answer 20

Pulmonary = lungs

Extra-pulmonary = larynx, LN, pleura, brain, kidneys, bones/joints

Miliary (uncontrolled bacterial spread) = all parts via bloodstream

Question 21

What are the risk factors to make you suspect TB?

Answer 21

Recent migrants/non-uk born

HIV

Homeless

Drug users

Close contacts

Question 22

What are the symptoms of TB?

Answer 22

Fever

Night sweats

Weight loss and anorexia

Tiredness and malaise

Cough (most common)

Haemoptysis occasionally

Breathlessness if pleural effusion

Question 23

What are the signs of TB?

Answer 23

Fever

Weight loss

Often no chest signs despite CXR abnormality

Lung crackles

Extensive disease = signs of cavitation, fibrosis

Signs of effusion

Question 24

Which investigation would be performed when TB is suspected?

Answer 24

CXR

3 morning sputum samples = solid/liquid cultures, ZN staining

Induced sputum = when pt cant bring up sputum

Bronchoscopy = tube into lungs, flush with saline, send fluid to lab (bronchi-alveolar lavage)

NAAT = nuclear acid amplification test, rapid result within a day

Drug resistant testing

Histology

Question 25

Why does Tb primarily effect the apex of the lungs?

Answer 25

Tb = obligate aerobe

Lung apex contains the most oxygen

Question 26

How does TB appear on an CXR?

Answer 26

Apex involved

Patchy consolidation

Pleural TB = pleural effusion

Fibrosis

Question 27

How is TB treated?

Answer 27

Anti TB drugs = rifampicin, isoniazid, pyrazinamide, ethambutol

Multi-drug therapy – 4 drugs

Vit D

Surgery

Question 28

What is MDR TB?

Answer 28

Resistant to rifampicin and isoniazid

Question 29

What is XDR TB?

Answer 29

Also resistant to fluoroquinolones and at least 1 injectable

Question 30

How does extra-pulmonary Tb present?

Answer 30

Lymphadenitis = cervical LNs most commonly, abscesses

GI = swallowing of tubercles

Peritoneal = ascites

Genitourinary = slow progression to renal disease

Bone/joints = potts disease

CNS = meningitis, chronic headache

Question 31

How can TB be prevented?

Answer 31

Notifiable disease = to public health England

Contact tracing

Provide surveillance data to detect outbreaks/monitor trends

Active case finding

-ve pressure isolation, PPE

Vaccination

Question 32

What is the BCG?

Answer 32

Live attenuated vaccine for TB

Only 70% effective

Question 33

Discuss the characteristics of TB

Answer 33

demonstrated by ziehl nielson stain

culture takes several weeks to grow

obligate aerobe

can survive dormant inside TB granulomata for years

Question 34

What are the risk factors for the reactivation of TB?

Answer 34

HIV infection

renal transplant

leukaemia

IV drug abuse

Question 35

Which MO causes atypical community acquired pneumonia?

Answer 35

mycoplasma pneumoniae