Tuberculosis: Microbiology of Diagnosis and Management

Question 1

50 year old Polish male

• 2/52 cough and weight loss
• GP gave amoxicillin – no improvement
• Attended A&E – sent home

What does this person?

Answer 1

Pulmonary TB

Question 2

23 year old male

• 1/12 hx fevers, headache, weight loss
• Vomiting, ataxia, clonus, leg weakness

Answer 2

Tb of the brain

Question 3

• 62 year old male, Sudanese
• 1 month history of fevers, rigors, lethargy and rapid weight loss - recent return from Sudan

Answer 3

Miliary Tb

Question 4

19 year old male

• 2/12 history of shortness of breath, fatigue, weight loss and vomiting

What does this person have?

Answer 4

Pericardial TB

Question 5

• 47 year old female

• Ascites, fevers, thickened peritoneum on CT

Answer 5

TB in the peritoneum - nodular pattern seen in omentum - rare

Question 6

• 20 year old, lives in Pakistan
• Came to UK November 2018
• 3/52 cough, fever, night sweats

What could this person have?

Answer 6

Bilateral lymphadenopathy

Causes: TB, sarcoidosis, lymphoma

Question 7

What is Tuberculosis?

Answer 7

Infection -Affects any part of the body -Curable (6 months of combination therapy) -Mycobacterium tuberculosis

Contagious -If affecting the lungs (pulmonary) -Transmission via airborne particles

Question 8

What happens when you get TB?

Answer 8

1. Nothing
2. Inhalation of TB organisms

Granuloma formation

• Macrophages engulf TB (“epithelioid histiocytes”)
• Fuse to form Giant Cells with central necrosis
• “Ghon Focus” (Lung)
• “Ghon Complex” (+LN)

Question 9

How is latent TB screened?

Answer 9

Latent TB Screening

1. Has this person been exposed to TB?
   a) Tuberculin Skin Test (TST)
   b) Interferon Gamma Release Assay (IGRA) i. QuantiFERON ii. T-Spot (used for those with immunocompromise)
2. Positive - check if they have active TB by seeing if they have symptoms of it
3. Negative - check BCG scar (only effective for 60% of cases)

Question 10

What is epidemiology of TB?

Answer 10

• ¼ of the worlds population is infected with TB (latent) – Globally 10 million people had TB (2017) (1%) – 1.4 million deaths (2017)
• TB as a cause of death – Number 1 amongst curable infectious diseases – One of the top 10 globally
• Associated with – poor sanitation – overcrowding – poverty
• Common in big cities such as Birmingham and London and South of England

Question 11

Symptoms and signs of TB

Answer 11

Long history (slow growing organisms) – Fever  Infection – Weight Loss & Fatigue  Prolonged inflammatory state – Night Sweats  TNF alpha

“Consumption”

• Cough / Haemoptysis / Abdominal Pain / Headache / Back Pain etc

Question 12

X ray and TB

Answer 12

Upper lobe consolidation, destruction of lung and millet seed pattern

Question 13

What are differential diagnosis of

Fever, Weight Loss, Night Sweats

What are differential diagnosis of granulomas?

Answer 13

 Cancer (Lymphoma, Leukaemia, Lung, Bowel, Metastasis)

 Infection (Bacterial / Fungal)

Granulomas:

 Sarcoidosis  Crohns Disease  Granulomatosis with Polyangiitis (GPA) Infection (Fungal / Parasitic)

Question 14

What is the treatment for TB?

Answer 14

– 6 months

• 2 months RIPE (Rifampicin, Isoniazid, Pyrazinamide & Ethambutol)
• 4 months Rifampicin & Isoniazid

Question 15

What is the treatment for drug resistance TB?

Answer 15

Drug resistant TB

– Longer (9-24 months) depending on the resistance pattern

• Mono/Poly resistance
• Multi-drug resistant (MDR) - (Rifampicin & Isoniazid)
• Extensively drug resistant (XDR) (MDR + Quinolones & Injectables)

Question 16

How do you diagnose TB

Answer 16

Think TB

Send sample to microbiology by doing any of the following:

– Sputum x 3 – Broncho-Alveolar Lavage (BAL) – Gastric Lavage – Blood – CSF – Tissue

Mycobacterium tuberculosis (ACID FAST BACILLI) Slow growing (15 – 20 hours to double)

“Acid Fast”  Neither gram positive or negative oHigh lipid content (Mycolic Acid) o Poor dye absorption but high retention

1. Auramine Stain (Auramine phenol)  fluorescent a) “smear positive” – highly infectious b) initial screening of sputum (done on same day)
2. Ziehl Neelson Stain (Carbol Fuchsin)  red on blue
   a) confirmation of Mycobacteria (takes a while)
   b) Can comment on morphology (TB vs NTM) -> if it is branching it is NTM rather than TB

Growing the organism

Conventional - takes 8 weeks grown yellow colonies check picture - after growing u use ZN stain

Liquid media - faster - 4 weeks - white snow flakes

Then do drug susceptibility to see which antibiotic to use.

Question 17

Microbiology behind

Answer 17

Mycobacterium

o Aerobic bacilli/rods (upper lobes) o >85 species

a) Mycobacterium Tuberculosis Complex (genetically linked) o Tuberculosis – human hosts o Bovis – cows and human hosts. Unpasteurized milk o Africanum, BCG
b) Mycobacterium leprae
c) Non-Tuberculos Mycobacteria (NTM)

o Environmental o Cause disease in immune-compromised patients o M avium-intracellulare (MAI)(HIV), M kansasii(bronchioectasis), M chimera(patients with heart bypass - water infected), M abscessus

Question 18

How do you test drug sensitivity?

Answer 18

Growt in different tubes and see which tube is reacting to it. As you see below it is not effective with isoniazid

Question 19

What is the limit of detection of ZN stain, auramine stain, Xpert MTB/RF, MGIT (liquid culture), solid culture

Answer 19

Considering Limits Of Detection and specimen volumes:

Xpert MTB/RIF might be 25-250 times less sensitive than MGIT culture

Question 20

What rapid test can you do to detect TB complex?

Answer 20

Whole Genome Sequencing (WGS) - really sensitive and specific

•WGS detects single nucleotide variations (polymorphism) (SNPs) 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

It allows you to network as well. It is used in Birmingham diagnostically but not other places in Uk apart from London

Question 21

Rapid test for TB

Answer 21

New technique:

. TB PCR (GeneXpert / Xpert MTB Rif / Cepheid)

– Straight from sputum

– Detects MTB complex (TB, Bovine, BCG etc)

– Can predict resistance to Rifampicin

• Do on high risk patients