Tuberculosis: microbiology of diagnosis and management Flashcards Preview

Yr 3 - December lectures 2018 > Tuberculosis: microbiology of diagnosis and management > Flashcards

Flashcards in Tuberculosis: microbiology of diagnosis and management Deck (22)
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1

What is tuberculosis?

infection caused by mycobacterium tuberculosis
- affects any part of the body
- curable following 6 months therapy

contagious
- if affecting the lungs - pulmonary
- transmission via airborne particles

2

What happens if you inhale TB organisms?

granuloma formation
- macrophages engulf TB (epithelioid histiocytes)
- fuse to form giant cells with central necrosis
- "ghon focus" = lung
- "ghon complex" = + lymph nodes

3

What is the difference between primary disease and latent infection?

primary disease = organisms continue to divide, poor immune systems

Latent infection = organism not dividing, sleeping/dormant TB

4

What does it mean by secondary TB?

latent TB reactivates
- organism wakes up and starts dividing
- decline in health and immunity

5

What are the latent TB screening methods?

Tuberculin skin test
Interferon gamma release assay (IGRA) - quantiferon and T-spot

If they react = do they have TB? if negative do they need BCG?

6

What is TB prevalence associated with?

poor sanitation
overcrowding
unpasteurized milk

7

What are the symptoms of TB?

Long history (slow growing organisms)
- fever => infection
- weight loss and fatigue => prolonged inflammatory state
- night sweats => TNF alpha
consumption
cough, haemoptysis, abdominal pain, headache, back pain

8

What are the differential diagnoses for the symptoms of TB?

fever, weight loss, night sweats
- cancer (lymphoma, leukaemia, lung, bowel, metastasis)
- infection (bacterial, fungal)

granulomas
- sarcoidosis
- crohn's disease
- granulomatosis with polyangitis
- infection (fungal, parasitic)

9

What is the treatment for TB?

RIPE
- rifampicin - 6 months
- izoniazid - 6 months
- pyrazinamide - 2 months
- ethambutol - 2 months

10

What is the main side effect of rifampicin?

bright orange urine

11

What are the treatments for drug resistant TB?

Longer = 9-24 months depending on resistance pattern
- mono/poly resistance
- multi drug resistant (MDR) = rifampicin and isoniazid
- extensively drug resistant (XDR) = MDR + quinolones and injectables

12

What microbiological samples need to be sent off to diagnose TB?

sputum x3
broncho-alveolar lavage
gastric lavage
blood
CSF
tissue

13

What are the features of mycobacterium tuberculosis?

aerobic bacilli (upper lobes) = acid fast (neither gram +ve or -ve- has a high lipid content (mycolic acid)), slow growing
>85 species
- mycobacterium TB complex = TB, bovis (cows and human hosts), africanum = BCG
- mycobacterium lepraw
- non-tuberculos mycobacteria (NTM) - environmental, cause disease in immunocompromised pts

14

How are acid fast stains used to diagnose TB?

1) auramine stain (auramine phenol) => fluorescent
- "smear positive" = highly infectious
- initial screening of sputum

2) ziehl neelson stain (carbol fuchsin) => red on blue
- confirmation of mycobacteria
- can comment on morphology

15

How can you grow TB?

1) solid media (conventional) => lowenstein jensen (only needs one organism)

2) liquid media (rapid) => MGIT (mycobacteria growth indicator tube) = needs 1-10 organisms)

16

What are the new developments to increase the speed of diagnosing TB?

1) TB polymerase chain reaction (PCR)
2) whole genome sequencing (WGS)

17

How does TB PCR work?

(geneXpert, Xpert, Cepheid)
- straight from sputum
- detects MTBc
- can predict resistance to rifampicin
diagnose same day and 2-4 weeks to determine drug resistance

18

What does WGS do?

detects single nucleotide variations (polymorphisms) between 2 isolates
TB mutates at 1 SNP every 2 years
- 0-5 SNPs difference between strains = most probably linked
- 5-12 SNPs may be linked
- >12 SNPs less likely to be linked

19

What are the benefits of WGS?

Faster drug susceptibility prediction
- more confident treatment regimens
- less likely to induce resistance
more informed contact tracing

20

Where does XDR most likely originate?

likely origin is E. Europe - within transmission in the UK

21

Where does MDR most likely originate?

likely origin is E. Africa

22

What is still needed in TB diagnostics?

WGS on sputum directly
smear negative
childhood Tb - sputum hard to get
biomarkers to detect LTBI with high risk of progression to active TB