L69 – Lower Respiratory Tract Infections II Flashcards Preview

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Flashcards in L69 – Lower Respiratory Tract Infections II Deck (78):
1

What is the gram staining of Mycobacterium tuberculosis?

Structurally Gram positive (exam) but not stained by the Gram stain

2

What stains can reveal Mycobacterium tuberculosis?

Acid-fast stains, e.g. Ziehl-Neelsen (ZN) stain

Fluorescent stains, e.g. auramine O

3

When is Fluorescent stains, e.g. auramine O used to stain M. tuberculosis?

Used to confirm Mtb:

 More sensitive than ZN for examination of clinical specimens
 But need confirmation** with ZN stain

4

What is the result of acid fast stain on Mtb?

blue background, red acid-fast bacilli

5

Is Acid fast bacilli = Mtb?

Definitely not ** important **

6

Mtb is susceptible to which abiotic factors as much as other non-spore-forming bacteria?

susceptibility to heat, ultraviolet light

7

Mtb is more resistant to which abiotic factors compared to other non-spore-forming bacteria?

 More resistant to drying
 Higher resistance to acids, alkalis, some chemical disinfectants

8

What chemicals are used to kill Mtb?

formaldehyde,
ethylene oxide,
70% ethanol
phenolics

9

What is the motility and spore formation of Mtb?

Non-motile, non-spore-forming

10

What are the 2 most important mycobacterial infections?

M. tuberculosis > tuberculosis
M. leprae > leprosy

11

What is the aerobic requirement of Mtb?

Obligate/ strict aerobe

12

Why does Mtb cause chronic infections?

Slow generation time: 16-18 hours

13

What is the culture for Mtb?

1) Egg-based medium:

** Löwenstein-Jensen (LJ) **medium > form breadcrumb colonies


2) Non-egg-based medium

14

What is the culture medium for M. bovis?

Stonebrink’s medium

15

Transmission of Mtb?

mostly airborne route (droplet nuclei) >> pulmonary
disease

16

Transmission of M. bovis?

ingestion (e.g. unpasteurized milk)

 Recall IASM: unpasteurized milk also contains Brucella

17

What is the difference between primary and post-primary tuberculosis?

Primary tuberculosis: after initial exposure, host immune response is absent until lymphocytes and macrophages are activated >> unrestrained bacterial multiplication

Post-primary tuberculosis (usually adults): reactivation, re-infection

18

What re the 2 sites of infection for Mtb?

 Pulmonary tuberculosis
(e.g. apex of lung common)

 Extrapulmonary tuberculosis (e.g. bone> Pott's puffy tumour)

19

Which of the 2 sites of Mtb infection is more common? Which one is more infectious?

Pulmonary tuberculosis is more common and infectious

Extrapulmonary tb is non-infectious and less common

20

What is the pathogenesis of Mtb? (think which WBC involved first)

1) Survive in macrophages

2) inhibit fusion of lysosomes with phagosome, but not actively dividing >> no host immune response yet

3) Cellular immunity and delayed hypersensitivity reaction (type IV) controls infection

4) Host immune response forms granulamatous inflammation and caseous necrosis

21

Does granulomatous inflammation occur in Mtb infecting an immunocompromised host?

No

Immunocompromised = less activated T cells = no gran. inflam.

22

What are the most useful and fastest diagnostic tools for Mtb?

-Acid fast stain (red bacilli on blue background)

-Culture>> use liquid media instead of solid media

-Tuberculin skin test

-In vitro gamma interferon release assays (IGRA)

- Histopathology

23

Difference between the 2 types of medium for cultureing Mtb?

Difference in speed

Solid media = 8-12 weeks

Liquid medium using automated culture and sensitivity testing = fast

24

What are some less sensitive/ effective ways to diagnose Mtb?

PCR > Not sensitive especially when bacteria load is low (e.g. when Mtb is dormant)

Antibody dectection is not useful for clinical diagnosis

25

What is obsevred in histopathology of Mtb?

 Granulomatous inflammation: activated T cells, macrophages
 Caseous necrosis, cavitation

26

How does Tuberculin skin test / Mantoux testwork?

 Intradermal injection of 0.1mL purified protein
derivative (PPD)

>> measure delayed-type hypersensitivity reaction to M.tuberculosis

27

What is a positive result for Tuberculin skin test?

positive if red induration achieves certain diameter

bleb; painful because tearing skin

28

What are some problems/ limitations of Tuberculin skin test?

 Cross-reaction with other mycobacteria

 Confounded by previous BCG vaccination

 Cannot distinguish past exposure / current infection

29

What is the difference in MoA between pyrazinimide and other anitbiotics?

Pyrazinimide = only one to kill Mtb by acid inhibition, can kill during dormancy

Others = only kill Mtb during **continuous growth, cannot kill during dormancy

30

What are the 1st line agents for Mtb? **important**

PRESI

Pyrazinamide
Rifampicin
Ethambutol
Streptomycin
Isoniazid

31

What are the 2nd line agents for Mtb?

FEC

 Fluoroquinolones (levofloxacin, moxifloxacin)

 Ethionamide

 Cycloserine

32

What is the name given to the tuberculosis (TB) control strategy recommended by WHO?

Directly observed treatment, short-course = DOTS

33

What is the duration of therapy for Mtb? Under what circumstances is it longer?

Minimum 4-6 months

Longer for:
 Infections of central nervous system, bones
 Patients who cannot tolerate standard first-line agents

34

What are the 3 strains of antibiotic resistant Mtb?

Multidrug resistant tuberculosis (MDR-TB)

Extensively drug-resistant tuberculosis (XDR-TB)

‘Totally drug-resistant tuberculosis’ (TDR-TB)

35

What is MDR-TB resistant to?

at least isoniazid and
rifampicin

36

What is XDR-TB resistant to?

 MDR-TB
 + any fluoroquinolone
 + at least 1 of 3 following injectable drugs: amikacin, kanamycin, capreomycin

37

What is the BCG vaccine?

Bacille Calmette-Guérin (BCG) vaccine
= attenuated strain of Mycobacterium bovis

38

How effective is BCG vaccine?

Highly variable protective efficacy in different populations:
 Against lung disease: 0-80%
 Against meningitis: 46-100%

39

Name other Mycobacterium that are not Mtb or M.leprae?

non-tuberculous mycobacteria (NTM):

atypical mycobacteria,

mycobacteria other than tubercle bacillus (MOTT)

environmental mycobacteria

40

What does M.marium infect?

causes skin, soft tissue infection after exposure to seawater

41

What are some rapid growth mycobacterium? FA

M. fortuitum, M. abscessus

42

What type of pathogen causes pneumocytosis? Transmission?

Pneumocystis jiroveci
= fungus (not protozoa)

Probably spread by inhalation

43

What is pneumocytosis?

commonly = pulmonary infection: pneumocystis pneumonia

44

What is the action of pneumocytis jiroveci?

colonize / asymptomatically infect the respiratory tract of normal healthy individuals

45

What are the 2 groups of patients affected by pneumocytis jiroveci?

- Non-HIV/AIDS patients

- HIV/ AIDS patients

46

What Non-HIV/ ADIS patients are commonly affected by pneumocytis jiroveci?

- Premature infants, malnourished or overcroswded children

- severely immunocompromised persons (e.g. transplant recipients, immunosprressive therapy)

47

Can pneumocytis pneumonia be used as an indicator disease of AIDS?

Yes
HIV/AIDS patients: 85% with pneumocystis pneumonia

48

What are the resultant infection, CXR and general symptoms of pneumocytis jiroveci?

Mostly pulmonary infections

CXR = bilateral diffuse infiltrates

Hypozaemia, fever, cough

49

What are some general pneumonia symptoms?

cough, sputum, reduced air entry, bronchial breath sounds, crepitations,
shortness of breath, respiratory failure

50

What are the 2 diagnostic tools for pneumocytis jiroveci causing pneumocytosis?

Microscopy using:

1) commonest = bronchoalveolar lavage

2) Induced sputum for HIV positive, immunosuppressed hosts

3) Rare = Transbronchial biopsy, open lung biopsy

** Expectorated sputum is not acceptable



51

What staining is done to diagnose p.jirocevi?

Methenamine silver stain or similar silver stains >> cup-shaped

52

What are the options of managing pneumocytosis?

1) Specific chemotherapy,

2) Chemophylaxis in high risk individuals, e.g. HIV/AIDS, transplant recipients

3) Respiratory support

53

Influenza is caused by which viruses?

influenza viruses:

Belong to Orthomyxoviridae

enveloped RNA virus

54

What is the structure of nucleoplasmid?

Nucleocapsid: segments of single-stranded RNA + RNA polymerase + nucleoprotein:

55

What is H and N in viruses?

Haemagglutinin

Neuraminidase

56

Functions of H and N in Influenzavirus A?

Haemagglutinin (HA, H): 18 types (H1-18)
 Attachment to host cells

Neuraminidase (NA, N): 11 types (N1-11)
 Facilitates release and spread of virus

57

What are the most commonly found influenzavirus A in humans?

H1N1

H3N2

58

Compare the nucleopasmid segments between the 4 types of Influenzavirus A?

A= 8 seg. of ssRNA
B = 8 seg
C and D = 7 seg

59

What is the nautral reservoir of inflenzavirus D?

Cattle

60

What is antigenic drift?

 Relatively minor changes
 Occur frequently within an influenza subtype (e.g. H1N1, H3N2)

61

What is antigenic shift?

 Major changes in antigenic composition >> appearance of a new HA or NA

 Can result in a pandemic if transmitted efficiently from person to person (e.g. 2009
pandemic H1N1pdm)

62

What does both antigenic shift and drift result in?

Ressortment and variation of viral genetic composition

63

What are the inflenza peak seasons in hong kong?

2 peak seasons:
1. Winter: February to March
2. Summer: July to August


Magnitude, duration of peak seasons vary from year to year

64

Trasmission of influenzavirus?

respiratory droplets (exam) >> local multiplication at respiratory epithelium

sometimes airborne

65

Incubation period of influenzavirus?

18-72 hours

66

When does viral shedding occur in influenzavirus?

day before to 3-5 days after onset of symptoms


Children: may be prolonged (up to 21 days)

67

What are the respiratory and systemic symptoms of influenzavirus?

 Respiratory: dry cough, nasal discharge

 Systemic (much more prominent than respiratory): headache, fever, myalgia, malaise

68

What is the respiratory complication of influenza?

primary viral (can be rapid progress) / secondary bacterial pneumonia

69

What is the systemic complication of influenza?

 Myositis, seizure, encephalopathy /encephalitis

Worsen Cardiopulmonary diseases

Reye syndrome (swelling in brain, liver)

70

What are the USEFUL clinical diagnostic tools for Influenza?

Molecular diagnosis via PCR

** Viral antigen detection: immunofluorescence staining, enzyme immunoassay (EIA),
immunochromatographic assays

Clinical diagnosis (symptoms, seasonality...etc)

71

What are some LESS usedful diagnostic tools for Influenza?

 Serology (generally not useful for clinical diagnosis because need paired sera)


 Viral culture (takes too long)

72

What are some general symptomatic treatments for influenza?

 Analgesics (relieve pain), antipyretics (prevent / reduce fever)

73

What drugs are avoided in children with influenza?

aspirin (Reye syndrome)

non-steroidal anti-inflammatory agents

74

Name some neuraminidase inhibitors?

oseltamivir (Tamiflu),

zanamivir (Relenza),

peramivir, laninamivir, Baloxavir

75

What are the 3 prevention methods against influenza?

Seasonal or pandemic influenza Vaccines

Chemopropylaxis

Infection control measures in institutions, health care facilities

76

What are the inactivated vaccines for influenza?

 Trivalent: 2 influenza A + 1 influenza B strain; or

 Quadrivalent: 2 influenza A + 2 influenza B strains

(Composition of vaccine strains is updated yearly)

77

Compare the administration between inactivated, live-attentuated and recombinant vaccines for influenza?

Inactivated vaccine:Intramuscular / intradermal administration

Live-attenuated vaccine: intranasal administration

Recombinant vaccine: intramuscular

78

What is administered in recombination vaccine for influenza?

recombinant haemagglutinin proteins

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