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2021-22 Clinical microbiology > W4 LRTI > Flashcards

W4 LRTI Flashcards

1
Q

Name some acute lower respiratory tract infections

A
  1. Pneumonia
  2. Bronchitis
  3. Bronchioloitis
  4. Legionnaires’ disease
  5. Whooping cough
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2
Q

Name some chronic lower respiratory tract infections

A
  1. Tuberculosis
  2. Aspergillosis
  3. Cystic fibrosis
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3
Q

What is pneumonia

A

An acute LRTI associated with recently developed radiological signs. Infection of the lungs due to bacteria, viruses and fungi

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4
Q

How can pneumonia be aquired?

A

May be acquired in the community (CAP) or in the hospital (HAP); associated risk factors

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5
Q

How many people die from pneumonia each year?

A
  • Approximately 30,000 people die due to pneumonia in the UK per annum
  • May present with either TYPICAL or ATYPICAL symptoms
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6
Q

What is peumonia caused by?

A

•May be caused by several organisms therefore accurate identification is essential to ensure appropriate antimicrobial therapy

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7
Q

How is pneumomia classified?

A
  • Community-acquired pneumonia (CAP)*
  • Hospital-acquired pneumonia (HAP)*
  • Aspiration pneumonia
  • Recurrent pneumonia
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8
Q

Describe Community Acquired Pneumonia (CAP)

A
  • Every year, 0.5% to 1% of UK adults will have CAP (approx. 320,000 – 640,000 people)
  • Mainly seasonal: Autumn / Winter
  • CAP is diagnosed in 5 to 12% of patients presenting to their GP with symptoms of LRTI
  • 22 to 42% admitted to hospital (approx.100,000 patients)
  • 5 to14% die in hospital
  • 50% of deaths occur in patients 84 years or more
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9
Q

What are the signs and symptoms of typical pneumonia?

A

Predominantly respiratory; most common in elderly; may occur spontaneously in young adults

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10
Q

What microorganisms are acquired with communiated associated pneumonia?

A

Most common:

  • Mycoplasma pneumoniae

Less common:

  • Legionella pneumophila (legionnaires disease)
  • Chlamydophila psittaci (psittacosis)
  • Chlamydophila pneumoniae

Don’t forget the viruses:

  • Influenza A/B
  • Rhinovirus
  • RSV
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11
Q

Show the radiological appearance of
TYPICAL and ATYPICAL pneumonia

A
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12
Q

Many organisms cause CAP: What are the associated risk factors

A
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13
Q

What is the 3rd most common hospital acquired infection?

A

Hospital acquired infection (HAI)

Patients may present with typical / atypical symptoms

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14
Q

What are the risk factors for HAP?

A
  1. Ventilatory support: Klebsiella pneumoniae, Pseudomonas aeruginosa (‘hospital flora’); VAP -48hrs or more following intubation
  2. Immunosuppression: organ transplantation: Aspergillus fumigatus
  3. Immobility and vomiting: aspiration pneumonia- oral bacteria eg. viridans streptococci and anaerobic bacteria
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15
Q

What regimens are available for the treatment of different types of pneuomia?

A
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16
Q

What organism is the most common cause of community acquired pneumonia?

A

S. pneumoniae

17
Q

Streptococcus pneumoniae mechanisms of Pathogenicity: Capsule

(Major virulence factor)

A
  • Antiphagocytic (evasion of immune attack)
  • 92 different capsular types; serotypes differ in virulence
  • 90% pneumonias are caused by about 23 serotypes (used in development of PPSV23)
  • Quellung reaction (serotyping with homologous antibody)
18
Q

Streptococcus pneumoniae mechanisms of Pathogenicity: CbpA adhesin

A

Major pneumococcal adhesin. The adhesin interacts with carbohydrates on the pulmonary epithelial surface

19
Q

Streptococcus pneumoniae mechanisms of Pathogenicity:

PspA (Protective Antigen)

A

Inhibits complement-mediated opsonization of pneumococci

20
Q

Streptococcus pneumoniae mechanisms of Pathogenicity:

IgA1 protease

A

Cleaves IgA1 the principal immunoglobulin isotype for the respiratory tract

21
Q

Streptococcus pneumoniae mechanisms of Pathogenicity:

Autolysins (LytA, LytB, LytC)

A

Breaks peptide cross linking in cell wall peptidoglycan releasing cell wall components; massive inflammation and pneumolysin release

22
Q

Streptococcus pneumoniae mechanisms of Pathogenicity:

Pneumolysin

A

Toxin released during autolysis; inhibits neutrophil chemotaxis, phagocytosis, lymphocyte proliferation and immunoglobulin synthesis

23
Q

Draw a diagram to show streptococcus pneumoniae
Mechanisms of Pathogenicity

A
24
Q

Diagnostic Clinical Microbiology: Case Study

Case: Streptococcus pneumoniae pneumonia

  • A 65-year lady presents to A/E complaining of breathlessness, chest pain and has a temperature
  • She reports that she has been ‘coughing up’ blood stained sputum for the last 5-days
  • Chest X-ray: widespread consolidation in both lungs
A
  • Initial Diagnosis: Community Acquired Pneumonia (CAP)
  • Most likely pathogens: Streptococcus pneumoniae, Haemophilus influenzae
  • Reasons for laboratory confirmation: Pneumonia is caused by a wide range of organisms; rapid identification of the pathogen and effective treatment is essential
25
Q

Case: Streptococcus pneumoniae pneumonia

Describe specimen collection and transport

A
  • Correct labelling of samples and form
  • Sputum (early morning, before breakfast) for microscopy culture and sensitivity
  • Gram stain (non culture technique)
  • Culture

•Urine (rapid pneumococcal antigen test)

-Antigen detection (non culture technique)

•Transport <24h

26
Q

Laboratory investigations for bacterial pneumonia: State the sample required

A

Sputum

27
Q

Laboratory investigations for bacterial pneumonia: State the non-culture technqiues

A

Sputum: Microscopy; Gram stain

28
Q

Laboratory investigations for bacterial pneumonia: State the non-culture technqiues state the culture technqiues

A

(a) Blood agar (37oC,5%CO2, 24h) + optochin disc
(b) Chocolate agar (37oC,5%CO2, 24h)

29
Q

Laboratory investigations for bacterial pneumonia: State the non-culture technqiues state the safety considerations

A
  • S. pneumoniae: category 2 pathogen
  • Sputum sample: category 3 laboratory; class I safety cabinet
30
Q

What are the safety aspects of a class I safety cabinet?

A

(a) Negative pressure, inward flow of air
(b) 0.74m3/sec air flow rate
(c) HEPA filter (high efficiency particle absorber)

31
Q

Describe the basic identification of Streptococcus pneumoniae

A
  • Colonial appearance: Strep pneumoniae grow as alpha-haemolytic colonies,1 mm in diameter, sometimes mucoid
  • Gram stain of colonies: Gram-positive diplococci
32
Q

How would you fully idetify Streptococcus pneumoniae?

A

• Optochin sensitivity: large zone (16mm) of inhibition around optochin disc: differentiates pneumococci from ‘normal’ oral streptococci

33
Q

S. pneumoniae antigen detection: Describe the non-culture technique

A

Immunochromatographic assay / lateral flow assay

SAMPLE: URINE

  • Rabbit-anti-Strep. pneumoniae bound to a nitrocellulose membrane
  • Urine added to test well; read result in 15 minutes
  • 86% sensitivity; 94% specificity
  • Diagnostic if positive; however a negative result DOES NOT rule out infection
34
Q

Describe EUCAST Sensitivity Testing / Treatment / Prevention

A
  • S. pneumoniae susceptible to penicillin also are susceptible to nearly all other antibiotics
  • Penicillin-Resistant S. pneumoniae (PRSP): strains have become increasingly prevalent worldwide; 50% PRSP
  • Drug-resistant S. pneumoniae (DRSP): now widespread eg. tetracycline, macrolides, trimethoprim-sulfamethoxazole

25% multi-drug resistant

•Fluoroquinolones remain active: moxifloxacin

35
Q

Describe PNEUMCOCCAL VACCINATION

A
  • At risk patients:

23-valent pneumococcal polysaccharide vaccine (PPSV23)

  • Childhood immunisation programme:
    2010: pneumococcal conjugated vaccine (PCV13)

(< 2 years of age; 4 doses)

36
Q

What are the key points of LRTI’s?

A
  • LRTI infections are acute or chronic and caused by a wide variety of microorganisms
  • Pneumonia may be CAP or HAP and may present with typical or atypical symptoms
  • Pneumonia is caused by many microorganisms / associated ‘risk factors’
  • Streptococcus pneumoniae the major cause of TYPICAL pneumonia; possesses a wide range of virulence factors to cause disease
  • Rapid laboratory confirmation is essential to ensure appropriate therapy
  • S.pneumoniae is becoming increasingly resistant to several antibiotics. Moxifloxacin is now recommended for treatment
  • Pneumococcal vaccination available

2021-22 Clinical microbiology (10 decks)

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