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ACEM Primary Written > Respiratory: Pathology - Pulmonary infections > Flashcards

Respiratory: Pathology - Pulmonary infections Flashcards

1
Q

Five common and one uncommon causative pathogens in community-acquired pneumonia. Which is most common?

A
  1. Streptococcus pneumoniae (most common)
  2. Haemophilus influenzae
  3. Moraxella catarrhalis
  4. Staphylococcus aureus
  5. Legionella pneumophila

Rarely:
1. GNRs (e.g. Klebsiella, Pseudomonas)

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2
Q

Three causative pathogens of atypical community-acquired pneumonia. Which of these is most common?

A
  1. Mycoplasma pneumoniae (most common)
  2. Chlamydia species
  3. Coxiella burnetti (Q fever)
  4. Viruses
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3
Q

Which viruses can cause atypical pneumonia in children vs adults?

A

Children: RSV, parainfluenza
Adults: influenza A and B, adenovirus, SARS

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4
Q

Three groups of typical causative organisms in hospital-acquired pneumonia

A
  1. Enterobacteriaceae (Serratia marscenens, Klebsiella, E. coli)
  2. Other GNRs including Pseudomonas
  3. Staphylococcus aureus (usually penicillin-resistant)
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5
Q

Typical causative organisms in aspiration pneumonia

A

Anaerobic oral flora (Bacteroides, Prevotella, Fusobacterium) mixed with aerobic species (Streptococcus pneumoniae, Staphylococcus aureus, Haemophilus influenza, Pseudomonas)

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6
Q

Three typical causative organisms in chronic pneumonia

A
  1. Nocardia
  2. Actinomyces
  3. Granulomatous (e.g. due to TB and atypical mycobacteria, Histoplasma capsulatum)
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7
Q

Typical organism mix in necrotising pneumonia and lung abscess

A

Anaerobic +/- aerobic mixed infection

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8
Q

Six causative organisms of pneumonia in immunocompromise

A
  1. CMV
  2. Pneumocystis jiroveci
  3. Mycobacterium avium complex
  4. Invasive aspergillosis
  5. Invasive candidiasis
  6. Other “typical” organisms
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9
Q

Give two examples of causative organisms in pneumonia for which there is a vaccine available

A

Streptococcus pneumoniae
Haemophilus influenza

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10
Q

What type of bacteria (Gram stain, morphology) is Haemophilus influenza?

A

Gram negative coccobacillus

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11
Q

What is the most common bacterial cause of COPD exacerbation?

A

Haemophilus influenzae

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12
Q

What other (important to recognise) condition does Haemophilus influenzae cause?

A

Life-threatening meningitis in young children

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13
Q

What other condition may be caused by Moraxella catarrhalsi?

A

Otitis media in children

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14
Q

Which organism confers a higher risk of complications of pneumonia?

A

Staphylococcus aureus

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15
Q

Which causative organism more commonly causes pneumonia in IVDU?

A

Staphylococcus aureus

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16
Q

What is the fatality rate of Legionella pneumonia?

A

Up to 50%

17
Q

What are the two patterns of distribution seen in pneumonia? Give a brief description of each

A

Bronchopneumonia: patchy exudative consolidation of lung parenchyma
Lobar pneumonia: fibrinosuppurative consolidation of large portion or entire lobe

18
Q

Describe the macroscopic and histological changes seen in bronchopneumonia?

A

Patchy exudative consolidation of lung parenchyma:
- Multiple consolidated areas of acute suppurative inflammation, with neutrophil-rich exudate filling airspaces
- Frequent bilateral and basal (due to effect of gravity on secretions)
- Lesions appear slightly elevated, dry, granular, grey-red to yellow in colour, and are poorly demarcated

19
Q

What organisms most commonly cause bronchopneumonia?

A

Staphylococci
Streptococci
Pneumococci
H. influenzae
Pseudomonas aeruginosa
Coliform bacteria

20
Q

Describe the four stages of response seen in lobar pneumonia

A
  1. Congestion: vascular engorgement and accumulation of intra-alveolar fluid occurring within first 24hrs
  2. Red hepatisation: massive confluent exudation (with neutrophils, RBCs and fibrin) produces gross appearance that is liver-like (hence “hepatisation”; looks red, firm, airless)
  3. Grey hepatisation: RBCs disintegrate but fibrinosuppurative exudate persists, gross appearance is now greyish-brown and dry
  4. Resolution: enzymatic and cellular degradation and clearance of exudate occurs; lung may undergo organisation leaving fibrosis and adhesions
21
Q

What organisms most commonly cause lobar pneumonia?

A

Pneumococci
Occasionally caused by Klebsiella, staphylococci, streptococci, Haemophilus)

22
Q

Four complications of pneumonia (more commonly lobar)

A
  1. Lung abscess
  2. Empyema
  3. Organisation of exudate into fibrotic scar tissue
  4. Bacteraemia, sepsis, and haematogenous seeding of other organs (including heart valves, pericardium, brain, kidney, spleen, joints)
23
Q

What was the term “atypical pneumonia” initially used to describe?

A

Acute febrile respiratory disease characterised by patchy inflammatory changes in lungs, largely confined to alveolar septa and pulmonary interstitium

24
Q

Why is “atypical” pneumonia so-called?

A

Produces atypical clinical presentation, with:
- Moderate sputum production
- No physical findings of consolidation
- Moderated WCC elevation
- Lack of alveolar exudate

25
Q

Describe the pathogenesis of atypical pneumonia

A

Organisms attach to upper respiratory tract epithelium and cause cell necrosis and inflammatory response
When process extends to alveoli, there is predominantly interstitial inflammation - however outpouring of fluid into alveolar spaces may produce CXR changes which mimic bacterial (lobar) pneumonia

26
Q

What has a higher mortality rate: typical or atypical pneumonia?

A

Typical

27
Q

Three morphological features of atypical pneumonia

A
  1. Predominance of interstitial pneumonitis: widened oedematous alveolar walls with mononuclear infiltrate
  2. Formation of hyaline membranes (reflects diffuse alveolar damage)
  3. Frequent superimposed bacterial infection
28
Q

What kind of virus is influenza?

A

Single-stranded RNA

29
Q

Describe the structure of influenzavirus and how this determines its classification and subtype

A

Single-stranded RNA virus, with RNA bound by nucleoprotein (determines classification: A, B or C)
Lipid bilayer envelope contains haemagglutinin and neuraminidase (determines subtype: H1-3, N1-2)

30
Q

Two mechanisms of infection clearance in influenza

A
  1. Cytotoxic T cells
  2. Intracellular anti-influenza protein (Mx1) induced in macrophages by IFN-a and IFN-B
31
Q

What phenomenon typically causes influenza epidemics vs pandemics?

A

Epidemics due to antigenic drift (mutations of haemagglutinin and neuraminidase)
Pandemics due to antigenic shift (haemagglutinin and neuraminidase replaced by recombination of RNA segments with those of animal viruses)

32
Q

What is a lung abscess?

A

Local suppurative process in lung charactered by necrosis of lung tissue

33
Q

In what % of lung abscesses is an oral anaerobe exclusively isolated?

A

60% (remainder are mixed infections)

34
Q

Five mechanisms whereby bacteria causing lung abscesses are introduced

A
  1. Aspiration (including dental sepsis, anaesthesia)
  2. Antecedent primary lung infection (usually Staphylococcus aureus, Klebsiella, or type 3 pneumococcus)
  3. Septic embolism
  4. Neoplasia (causing obstruction)
  5. Other (including direct trauma penetration, haematogenous spread, and spread from neighbouring organs)

ACEM Primary Written (150 decks)

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