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PPS - infections > Comorbidities > Flashcards

Comorbidities Flashcards

1
Q

What are the 3 diagnostic techniques used in TB?

A

Clinical history

Imaging - x-ray, CT

Microbiological investigations

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2
Q

What are examples of microbiological investigations used in TB?

A

Smear

Nucleic acid amplification tests

Culture

Antimicrobial susceptibilities of isolated mycobacterium tuberculosis

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3
Q

Why can samples for diagnosing TB be taken from many parts of the body?

A

TB can infect virtually anywhere, so samples received in the laboratory are varied

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4
Q

What are examples of sample types that can be taken to diagnose TB?

A

Pulmonary samples

Lymph nodes

Renal/Bladder

CSF

Biopsy or fluid aspiration from bone, joints, liver and other organs

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5
Q

When are pulmonary samples taken?

A

In cases of pulmonary TB

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6
Q

What are examples of pulmonary samples?

A

Sputum

Bronchoalveolar lavage/ washing

Pleural fluid

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7
Q

What are ways to obtain samples from the lymph nodes?

A

Lymph node dissection - excised entirely

Lymph node biopsy - fine needle aspirate

Imaging-guided biopsy

EBUS - endobronchial ultrasound biopsy of medisastinal nodes

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8
Q

Where are the mediastinal lymph nodes?

A

Center of the chest

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9
Q

What sample is taken from the renal/bladder?

A

Early morning urine samples

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10
Q

Why is CSF taken?

A

TB can cause meningitis and brain abcesses

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11
Q

Why are bone, joints and liver biopsies/aspirations taken?

A

As TB can go anywhere

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12
Q

M. tuberculosis is notoriously difficult to isolate and grow

TRUE or FALSE

A

TRUE

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13
Q

What are the difficulties in isolating M. tuberculosis?

A

Samples are often contaminated with other organisms

Some patients will not be able to produce sputum

Slow-growing organism

Samples are often paucibacillary

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14
Q

What happens if the patients are unable to produce sputum?

A

Bronchoscopy

Induced sputum

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15
Q

How can you induce sputum?

A

Inhale nebulised saline

Irritates the lung

Induces the production of sputum

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16
Q

How much time is needed for the M. tuberculosis to divide?

A

16-20 hours

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17
Q

What does paucibacillary mean?

A

Having or made up of few bacilli

Low number of organisms to start with

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18
Q

What type of organism is M.tuberculosis?

A

Hazard group 3

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19
Q

Which laboratory handles M. tuberculosis?

A

Containment level 3 laboratory

  • Special airflow
  • Equipment
  • Filters
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20
Q

What does a hazard group 3 organism mean?

A

Has potential to cause severe disease

Poses risk to people handling it
Potential to spread to people

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21
Q

How is the sample prepared for investigation?

A

Samples received have low numbers of bacteria

Need to concentrate by centrifugation to maximise yield

Non-sterile specimens are decontaminated to lyse other organisms

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22
Q

What is a smear?

A

Small proportion of concentrated sample

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23
Q

How is the smear prepared to be investigated?

A

Sample heat-fixed to microscope slides

Stained with a fluorescent stain such as auramine-O

Decolourise with 0.5-1% acid alcohol

Examine with a fluorescent microscope at x200-400 magnification

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24
Q

What is the purpose of decolorising the smear with acid alcohol?

A

Mycobacteria have lipid-rich walls

Pick up stain and retain them

If you see a fluorescent bacteria with microscope = definitely mycobacteria

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25
Q

What are the advantages of fluorescent microscopy?

A

Easy to screen

Better sensitivity than routine microscopy

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26
Q

All TB patients are smear-positive

TRUE or FALSE

A

FALSE

Around 90% are

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27
Q

What indications do smear-positive smears indicate about TB?

A

More likely to be infectious

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28
Q

What is done after a smear test comes back positive?

A

Get patient to treatment

Make sure not pass to other people

Quantify how positive a sputum slide is

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29
Q

What are the two procedures in which NAAT can be used to determine the antimicrobial susceptibility of the bacteria?

A

Genexpert

Genotype MTBDRplus

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30
Q

What does Genexpert consist of?

A

Mini PCR laboratory inside a blue box

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31
Q

How is the sample added to the Genexpert machine?

A

Take out concentrated decontaminated sample

Put in front of machine within 24 hours

32
Q

What two things does the Genexpert machine determine?

A

Determines whether M. tuberculosis is present

Tells us by looking at specific gene sequences if the organism is susceptible to a specific antibody

33
Q

How is the sample added to the Genotype MTBDRplus machine?

A

Concentrated and decontaminated sample is amplified using PCR

Nitrocellulose membrane with small sections of DNA bound to it

34
Q

What does Genotype MTBDRplus test for?

A

Look for 3 specific genes involved in antibiotic resistance

Those genes are amplified

35
Q

What is the positive result for the presence of resistance genes in Genotype MTBDRplus?

A

Blue line

36
Q

What is the gold-standard for diagnosing M.tuberculosis?

A

Culture

37
Q

What is the main disadvantage of culture?

A

Slow process

Takes 8 weeks

38
Q

What is a culture method used to grow TV?

A

Lowenstein Jensen media

Egg-based medium

Concentrated decontaminated sample is inoculated onto the medium

39
Q

What is a modern culture method?

A

Mycobacteria growth indicator tube system

Fluorescent indicator flags when something grows in the tube

40
Q

How does Mycobacteria growth indicator tube system work?

A

Fluorescent is bound to oxygen

As bacteria grows and divides, uses the oxygen and disassociates it from the fluorescent molecule

Sensor detects when something is growing

Analyser flags when something grows in the tube

41
Q

What type of growth medium is used in the Mycobacteria growth indicator tube system?

A

Liquid culture

42
Q

What are the advantage of Mycobacteria growth indicator tube system?

A

Machine reads the growth automatically

Less input from a scientist

Growth time is faster in liquid media

43
Q

What is another method of detecting the presence of M. tuberculosis?

A

Colour indicator on bottom

CO2 produced by bacteria that divide and respire

Drops the pH of the tube

Every 10 minutes - pH is detected

The colour of the indicator changes accordingly

44
Q

What proportion of TB cases are multi-drug resistant?

A

5% of cases

45
Q

What two drugs indicate MDR-TB?

A

Rifampicin

Isoniazid

46
Q

What if TB is only resistant to Isoniazid?

A

It is not considered MDR-TB

47
Q

What are four ways in which patients acquire MDR-TB?

A

Infected with a resistant strain

Poor compliance

Poor absorption

Interactions with other drugs causing subtherapeutic levels

48
Q

What is the amount of time patients with TB have to take medication?

A

6 months

49
Q

Why may patients not comply with the drug schedule?

A

Side-effects may make them stop taking the drugs since they feel better

50
Q

What are the two ways to detect resistance?

A

Phenotypically

Genotypically

51
Q

Why is it important to detect resistance in the population?

A

Make sure the patient is on correct treatment

Make sure the drug resistant strains don’t spread

52
Q

What is the phenotypic method for detecting resistance?

A

Isolates of M. tuberculosis are incubates in the presence of anti-TB drugs

Gives absolute definite idea whether strain is susceptible

53
Q

What are the pros of phenotypic testing for detecting resistance?

A

Gold-standard result

Know that organism growing is categorically susceptible or resistant to antimicrobial agent

54
Q

What are the cons of phenotypic testing for detecting resistance?

A

Takes time - weeks needed to know if the patient is on the correct treatment

Need to isolate - 1/3 of cases can’t

Need laboratory facilities

55
Q

What does the genotypic testing for detecting resistance entail?

A

Detect mutations on genes that may confer resistance

56
Q

What are the pros of genotypic testing?

A

Speed - hours

Can be performed on samples - no need to grow

57
Q

What are the the cons of genotypic testing?

A

Less accurate than phenotypic methods

Many gene mutations may not cause resistance

Phenotypically can confer resistance whilst genotypically can be susceptible

58
Q

What is the most sensitive method of diagnosing TB?

A

Culture > NAAT > smear

59
Q

Why is NAAT less sensitive in diagnosing TB?

A

Lipid wall is very thick

Difficult to obtain the RNA

PCR not as effective

60
Q

Why is it important to test for Mycobacteria TB specifically?

A

Over 130 species of mycobacteria

Downstream tests needed to confirm it is tuberculosis

61
Q

Why is TB called the great imitator?

A

A lot of symptoms overlap with other diseases

62
Q

What are methods of monitoring TB after diagnosis and treatment?

A

Smear conversion

Culture conversion

Detection of acquired resistance

63
Q

What is the process of smear conversion?

A

Look for the reduction of bacteria in smear

Gives an idea of how the treatment is going

If the sputum that is coughed up contains less bacteria = antibiotics are effective

64
Q

What is the main disadvantage of smear conversion?

A

Arbitrary system

Quantifying the number of bacteria is difficult

Quality of sample differs between periods of taking the samples

Not absolute

65
Q

What is culture conversion?

A

Look for not being able to grow the bacteria in the sputum of the patient

66
Q

How can we detect acquired resistance?

A

Need to find out why bacteria are resistant

Sensitive stains may have acquired resistance due to

  • poor compliance
  • poor absorption of antibiotics
67
Q

How are the patients managed following TB diagnosis?

A

Anti-tuberculosis treatment

Clinical and microbiological improvement

68
Q

What anti-tuberculosis treatment is used?

A

Empirical first

Modified based on drug susceptibility tests

69
Q

How is clinical and microbiological improvement tested for?

A

Smear and culture conversion

Improvement in clinical well-being

Look for

  • improvement of inflammatory markers
  • weight gain
  • improvement of imaging
70
Q

What inflammatory markers are used to look for clinical and microbiological improvement?

A

White cell count

C-reactive protein levels

71
Q

What is seen when patients improve in CXR?

A

Consolidations or cavities improve

72
Q

What are other important infections in HIV?

A

Oral candidiasis

Mycobacterium avium

PCP

73
Q

What is PCP?

A

Pneumocystitis jiroveci pneumonia

Fungal disease

74
Q

What is oral candidiasis?

A

Yeast that can grow abundantly in the mouth

75
Q

What is Mycobacterium avium?

A

Severe intestinal disease

Disseminated disease like sepsis in advanced HIV

PPS - infections (8 decks)

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