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4.1 Medical Microbiology > Tuberculosis > Flashcards

Tuberculosis Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Write a note on the frequency of TB according to the WHO Global TB Report 2020
(7)

A

TB is the leading cause of death from a single infectious agent

In 2020 there were 10 million cases and 1.4 million deaths

8.2% of cases were in people with HIV

500,000 people developed rifampicin-resistant TB (RR-TB)

78% of (RR-TB?) people had multidrug-resistant TB (MDR-TB)

3.3% of new TB cases and 17.7% of previously treated cases had MDR/RR-TB

Covid-19 pandemic threatens to reverse recent progress in reducing the global burden of TB

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2
Q

What is the most recent worldwide study on TB?

A

WHO Global TB Report 2020

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3
Q

How many cases of TB were there in 2020 and how many deaths?

A

10 million cases and 1.4 million deaths

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4
Q

How many cases of TB were there in 2020 and how many deaths?

A

10 million cases and 1.4 million deaths

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5
Q

Of the 10 million cases of TB in 2020, what percentage of these patients had HIV?

A

8.2% of cases were in HIV patients

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6
Q

Out of the 10 million cases of TB in 2020, how many developed rifampicin-resistant TB

A

500,000 people developed RR-TB

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7
Q

Out of the 500,000 cases of RR-TB in 2020, what percentage had multidrug-resistant TB

A

78% had MDR-TB

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8
Q

What is defined as multi-drug resistant TB?

A

Resistance to at least both isoniazid and rifampicin

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9
Q

What percentage of the 10 million cases of TB in 2020 were MDR TB?

A

3.3% of newly diagnosed cases were MDR

17.7% of previously treated cases were MDR -> rate of multi-drug resistance increases with failure to complete antiboitic course etc etc

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10
Q

According to the WHO 2020 report, how many estimated patients never get diagnosed or treated with TB?
Why is this significant?

A

WHO estimates that over 4 million cases of TB are not diagnosed or treated a year

Suggests there could by potentially 4 million infectious patients acting as a reservoire for potential spread

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11
Q

According to the WHO report of 2020, what percentage of resistant TB cases are detected?

A

Less than 25% of resistant cases are detected

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12
Q

Where in the world is there a significant burden of TB

A

Mostly Africa
Other third world countries where there is overcrowding etc e.g. India

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13
Q

What are the 6 main reasons why TB has not gone away?

A

HIV epidemic
Immigration
Increased poverty
Non compliant drug-therapy
Overcrowding
Latent tuberculosis

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14
Q

How has the HIV epidemic affected TB rates?

A

The HIV epidemic resulted in a large population of immunodeficient patients which were more susceptible to picking up TB

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15
Q

How has immigration affected TB rates?

A

There has been an increase in immigration from countries such as Africa and India where there is a much higher prevalence of TB

People from other countries entering Ireland with TB, increasing our stats as well as causing spread of disease to Irish population

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16
Q

How has an increase in poverty affected TB stats?

A

Increased poverty -> increase in homelessness -> increase in intraveous drug use

Think of homeless in Mater getting TB from rats and pigeons due to living conditions etc

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17
Q

How does non-compliant drug therapy affect TB stats?

A

Course of antibiotics between 6 and 9 months
Very difficult for patients to finish
Not finishing course of antibiotics results in TB returning or multi-drug resistant TB -> patient remains reservoire -> spread to others etc

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18
Q

How does overcrowding affect TB stats?

A

Overcrowding in prisons -> low socioeconomic inmates -> only need 1 with TB to spread to a lot of other prisoners etc
Overcrowding in hospitals -> spread to nearby patients etc -> immunocompromised patients etc

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19
Q

How does latent TB affect TB stats?

A

Latent TB stays in the lung as a granuloma
Latent TB can become reactive at any point in life
Potentially infectious individuals

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20
Q

What countries are most affected by TB?
(according to WHO)

A

India
Indonesia
China
Philippines
Pakistan
Nigeria
Bangladesh
Democratic republic of congo

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21
Q

Out of the 10 million TB cases in 2020, 8.2% were in HIV patients, where was the burden of these cases?

A

Over 50% of these 8.2% of cases were in Southern Africa

=> Over 4% of worlwide cases of TB were in HIV patients in southern Africa

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22
Q

Write a note on TB in Ireland based on the most recent study in 2019
(9 points of information)

A

267 TB cases
Incidence rate of 6.7 per 100,000
Incidence rate of 10.2 in those over 65 years old
40% are Irish born
44% are foreign born cases
Only 196 (73%) cases are culture positive
~10%/27 cases were resistant (5 MDR and 5 mono RF)
1 meningitis case caused by M.bovis
6 TB outbreaks

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23
Q

What was the total number of TB cases in ireland in 2019?

A

267 TB cases

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24
Q

What is the incidence rate of TB in Ireland?

A

Incidence of 6.7 per 100,000

This increases to 10.2 in those over 65 years old

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25
Q

Out of the 267 TB cases in ireland in 2019, what percentage were irish orn vs foreign born?

A

40% were irhs and 44% were foreign born

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26
Q

Out of the 267 TB cases in Ireland in 2019 what percentage of these were culture positive?

A

196/267 were culture positive = 73% were culture positive

Could have potentially missed 71 cases if only traditional culture used

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27
Q

Out of the 276 cases of TB in ireland in 2019, how many of these were resistant

A

27 of these cases were resistant
5 of these were MDR
5 of these were mono Rf

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28
Q

How many TB outbreaks were there in 2019 in ireland

A

6 outbreaks

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29
Q

Comment on the rates of TB over the years in Ireland

A

TB numbers have been steadily decreasing e.g. from nearly 400 in 2013 to justo ver 200 in 2021

There was a slight increas in 2022 but not above pre-pandemic levels

i.e. downward trend in TB cases in Ireland

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30
Q

Talk about the trends in drug resistant TB in Ireland over the years

A

Numbers always small but resistance is definitely increasing

e.g. only 4 MDR-TB and 1 XDR-TB in 2013 vs 8 MDR-TB, 4 mono Rf-TB and 2 pre-XDR cases in 2022

Doubled

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31
Q

List and explain the different kinds of resistance in TB
(Got these online, american version, who guidelines in layer flashcard)

A

mono RR-TB: TB resistance against rifampicin only

MDR-TB: Multi-drug resistant TB (rifampicin and isoniazid)

Pre-XDR TB: isoniazid, rifampicin and a fluoroquinolone OR a second line injectable (amikacin, capreomycin and kanamycin)

XDR-TB: extensively drug resistant TB -> isoniazid, rifampicin, a fluoroquinolone AND a second line injectible OR isoniazid, rifampicin, a fluoroquinolone and bedaquiline or linezolid

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32
Q

Explain what is Pre-XDR TB

A

Resistance against isoniazid, rifampicin and a fluoroquinolone OR a second line injectable (amikacin, capreomycin and kanamycin)

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33
Q

Explain what is Pre-XDR TB

A

Resistance against isoniazid, rifampicin and a fluoroquinolone OR a second line injectable (amikacin, capreomycin and kanamycin)

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34
Q

What are the second line injectables used to treat TB?
(3)

A

Amikacin

Capreomycin

Kanamycin

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35
Q

What is meant by XDR TB?

A

extensively drug resistant TB

Resistance against isoniazid, rifampicin, a fluoroquinolone AND a second line injectible

OR resistance against isoniazid, rifampicin, a fluoroquinolone and bedaquiline or linezolid

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36
Q

Write a short note on the Mycobacterium species

A

Acid-fast characteristic feature
Over 90 species identified
Characteristic cell wall

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37
Q

What is mean by acid-fast

A

When Mycobacterium is stained with a basic dye it cannot be decolourised subsequently with dilute acids

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38
Q

Write a note on the mycobacterium cell wall

A

Acid fast
Major determinant of virulence
Unique stucture
Unique lipid fraction (lipid section of wall)
Role in resistance

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39
Q

Write a note on the mycobacterium cell wall

A

Acid fast
Major determinant of virulence
Unique stucture
Unique lipid fraction (lipid section of wall)
Role in resistance

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40
Q

What makes the cell wall of mycobacterium unique?

A

Presence of peptidoglycan and complex lipids
High lipid content - can be up to 60% of wall
Hydrophobic and waxy

This waxy wall takes a lot of nutrients to develop and is one of the reasons why mycobacterium takes so long to grow

41
Q

What are the three main components of the mycobacterium lipid fraction of the cell wall

A

Mycolic acids
Cord factor
Wax-D

42
Q

What is the role of mycolic acids in the lipid fraction of the mycobacterium cell wall?

A

These allow the bacterium to grow inside macrophages -> immune evasion

Essential for the pathogenisis of tuberculosis and leprae

These are also whats resposible for the acid-fast property of the wall

43
Q

What is the role of mycobacterium waxy cell wall in resistance?

A

Makes organism resistant against antibitoics

Resistance against phagocytosis

44
Q

What is the role of cord factor in the cell wall of mycobacterium?

A

Cord factor is a major component of the cell wall

It is toxic to mammalian cells

It inhibits phagocytosis

Cord factor induces the formation of granulomas

Major virulence factors -> M. TB without cord factor are avirulent and virulent strains which loose their ability to produce cord factor loses its virulence

45
Q

How does Cord factor prevent phagocytosis?

A

Cord factor prevents the fusion between phagosomal vesicles containing the M, tubercuosis cells and the lysosomes that would destroy them

This allows M.TB to survive within immune cells

46
Q

What is the role of Wax-D in the waxy cell wall of Mycobacterium?

A

Role in resisting phagocytosis

47
Q

How does Wax-D prevent phagocytosis?

A

Regulates internal acidity by preventing hydrogen ion entering the phagosome -> ensures bacterial DNA replication

Prevents oxidation burst inside the phagosome (i have no idea what this means)

48
Q

What does MTC stand for?

A

Mycobacterium tuberculosis Complex

49
Q

What does NTM stand for?

A

Non Tuberculous mycobacteria

50
Q

What does NTM stand for?

A

Non Tuberculous mycobacteria

51
Q

Give some examples of mycobacterium that are part of the mycobacterium tueberculosis complex

A

M. tuberculosis
M. bovis subspecies bovis
M. bovis subspecies caprae
M. bovis BCG

52
Q

Write a note on M tuberculosis
(5)

A

An acid fast bacillus
Highly contagious
Aerosolised droplets
Mainly affects lungs but can affect any organ
1/3 people carry latent infection worldwide (1 in 4 irish) -> 10 percent may develop an active infection

53
Q

Write a note on M tuberculosis
(5)

A

An acid fast bacillus
Highly contagious
Aerosolised droplets
Mainly affects lungs but can affect any organ
1/3 people carry latent infection worldwide (1 in 4 irish) -> 10 percent may develop an active infection

54
Q

It is estimated that what percentage of people carry latent M. tuberculosis?

A

1 in 3 carry latent M TB infection worldwide
1 in 4 in Ireland (Cant find stats for this)

55
Q

It is estimated that what percentage of people carry latent M. tuberculosis?

A

1 in 3 carry latent M TB infection worldwide
1 in 4 in Ireland (Cant find stats for this)

56
Q

What percentage of latent MTB will become active at some point in life?

A

10% will become active

57
Q

What percentage of latent MTB will become active at some point in life?

A

10% will become active

58
Q

what are the five main symptoms of M. TB

A

Chronic cough
Haemoptysis -> blood in sputa
Drenching night sweats
Weight loss
Pyrexia

59
Q

What marks the formation of latent TB

A

Formation of granulomas in the lung

This happens when immune system is unable to clear infection -> TB resides in these granulomas -> can be reactivated at any point

60
Q

How long will a person have latent TB for?

A

Latent TB is lifelong

61
Q

How long will a person have latent TB for?

A

Latent TB is lifelong

62
Q

How can you test to see if a person has TB?

A

TST Skin test
Chest X ray
Interferon gamma

63
Q

What is the skin test for TB?

A

Mantoux tuberculin skin test (TST)

Involves injecting purified protein derivative (PPD) solution and measuring the size of the welt/swelling

64
Q

What is the interferon test for M. TB?

A

Interferon Gamma Release Assay (IGRA)

A blood test used to see if person infected with M TB

Measures bodys immun response to TB

65
Q

After exposure to M TB, how would you prove a person TB negative?

A

Negative TST or IGRA

Patient does not develop latent TB (X ray clear of granulomas)

Patient does not devlop TB disease

Patient not infectious

66
Q

After exposure to M TB, how would you prove a person TB negative?

A

Negative TST or IGRA

Patient does not develop latent TB (X ray clear of granulomas)

Patient does not devlop TB disease

Patient not infectious

67
Q

After exposure to MTB how would you prove a person has latent TB

A

Positive TST or IGRA

Normal chest radiograph -> no TB Disease

Latent TB -> might develop symptoms later in life but not currently infectious

68
Q

After exposure to TB, how would you prove a person has a MTB infection?

A

Positive TST or IGRA

Abnormal chest radiograph - evidence of TB disease

Symptomatic patient

Positive culture -> might have to wait a few weeks

Patient has TB disease and is infectious

69
Q

What would be a good sign a TB patient will be culture positive?

A

If interferon gamma positive

70
Q

In general what is active TB?

A

Positive skin test/interferon gamma, positive sputum, positive xray

71
Q

What are the different stages of TB

A

Primary tuberculosis (infection beginning usually STS and xray negative)

Progressive primary (active) infection (STS, xray and sputum positive)

Latent-dormant tuberculosis (sts positive but xray neg)

Secondary (reactivation) tuberculosis (sts, xay and sputum positive)

72
Q

What are the different stages of TB

A

Primary tuberculosis (infection beginning usually STS and xray negative)

Progressive primary (active) infection (STS, xray and sputum positive)

Latent-dormant tuberculosis (sts positive but xray neg)

Secondary (reactivation) tuberculosis (sts, xay and sputum positive)

73
Q

What are some risk factors for TB?

A

Exposure to an individual with active TB
Large infecting dose
Age and gender
Health conditions
Malnutrition
Smoking, silicosis
Occupation
Immune condition
Stress

74
Q

How is infectious dose a risk factor for TB?

A

A large infectious dose means you are more likely to be infectious

75
Q

How is infectious dose a risk factor for TB?

A

A large infectious dose means you are more likely to be infectious

76
Q

What health conditions are risk factors for TB

A

Leukaemia
Hodgkins Disease
Diabetes Mellitus
Alcoholism
IV drug abuse

77
Q

What aspects of malnutrition are risk factors or TB

A

Low body weight
Vitamin D deficiency

78
Q

What aspects of malnutrition are risk factors or TB

A

Low body weight
Vitamin D deficiency

79
Q

What immune conditions are risk factors for TB?

A

Immunosuppression
Corticosteroid treatment

80
Q

What are the requirements for a TB diagnosis?
(5)

A

Cough for 3+ weeks with at least one additional symptom

Any patient at high risk of TB with unexplained illness including respiratory symptoms of 3+ weeks

Any HIV patient with unexplained cough and fever

Any high risk patient with a diagnosis of CA pneumonia who has not improved after seven days of treatment

Any high risk patient with incidental findings on chest X ray suggestive of TB even if symptoms are minimal or absent

81
Q

Talk about the microbial investigation of MTB

A

Microscopy -> cheap and fast but limit of detection not great, negative microscopy doesnt always mean negative patient, positive miroscopy is definitely positive

NAAY -> nucleic acid amplification test -> best method

Culture -> very slow, takes about 8 weeks (clinicians usually start treatment while awaiting culture)

82
Q

What are three extra pulmonary forms of TB?

A

Lymphadenitis

Miliary TB

Tuberculosis Meningitis

83
Q

What are three extra pulmonary forms of TB?

A

Lymphadenitis

Miliary TB

Tuberculosis Meningitis

84
Q

What is lymphadenitis in TB?

A

This is where TB has spread to the cervical lymph nodes

85
Q

What is miliary TB?

A

This is where TB has spread to the blood
Will see infected lesions on X ray
Millet seeds (tiny tubercles)
Progressive Disseminated Haematogenous TB

86
Q

What is miliary TB?

A

This is where TB has spread to the blood
Will see infected lesions on X ray
Millet seeds (tiny tubercles)
Progressive Disseminated Haematogenous TB

87
Q

What is tuberculosis meningitis

A

This is where TB crosses the blood/brain barrier

Not really seen in Ireland -> 1 case in 2019 -> more of a problem in other countries

88
Q

What are the first line anti tuberculosis drugs?

A

Isoniazid
Rifampicin
Pyrazinamide
Ethambutol

89
Q

What are the main side effects of rifampicin?

A

Many drug interactions, check for any other medication

Discoloration of urine and contact lenses

Hepatotoxic

90
Q

What are the main side effects of isoniazid?

A

Pyridoxine (Vit B6) must be given to prevent INH (isoniazid) induced neuropathy

Hepatotoxic

91
Q

What is the main side effect of pyrazinamide?

A

Hepatotoxic

92
Q

What is the main side effect of pyrazinamide?

A

Hepatotoxic

93
Q

What are the main side effects of ethambutol

A

Risk of ocular toxicity
Must check baseline renal function
Regular visual acuity and colour discrimination

94
Q

What are the main side effects of ethambutol

A

Risk of ocular toxicity
Must check baseline renal function
Regular visual acuity and colour discrimination

95
Q

What are the two main concerns with antimicrobial treatment for MTB

A

Patients have to take medications for 6 to 9 months -> problems with compliance

Long course -> hepatic toxicity

96
Q

What is the work-around if there is concerns over anti-microbial compliance?

A

DOTS -> direct obsrved therapy

Done either inpatient or over video call -> clinician has to watch patient take medication

Much shorter course

97
Q

What is the WHO definition of RR-TB

A

TB resistant to rifampicin detected using phenotypic or genotypic methods with or without resistance to other anti-TB drugs

98
Q

What is the WHO definition of XDR TB

A

TB which are MDR-TB and also resistat to any fluoroquinalone and at least one additional group A drug (loveofloxacin, moxifloxacin, bedaquilline and linezolid)

99
Q

What does WHO class as group A drugs?
(4)

A

Levofloxacin
Moxifloxacin
Bedaquiline
Linezolid

4.1 Medical Microbiology (30 decks)

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