Pneumonia

Question 1

Site of infection

Answer 1

Lower respiratory tract - Lung parenchyma

Question 2

Types of causative pathogens

Answer 2

1) Bacterial pneumonia
- Most common
2) Fungal/Viral pneumonia
- Less common
- Fungal pneumonia usually only occurs in immunocompromised patients

Question 3

Pathogenesis

Answer 3

Bacteria can enter lower respiratory tract via:

1) Aspiration of oropharyngeal secretions
- Usually in patients with impaired cough reflux (e.g. stroke patients)
2) Inhalation of aerosols containing bacteria
3) Hematogenous spread
- Bacteria from extra-pulmonary source gets into bloodstream (bacteremia) and spreads to lungs

Question 4

Epidemiology in SG

Answer 4

3rd most common cause of hospitalization
Most common infectious cause of hospitalization
Most common cause of death due to infectious disease

Question 5

Clinical presentation & Diagnosis - Signs & symptoms

Answer 5

1) Cough, chest pain
2) Fever > 38oC
3) SOB, hypoxia
4) Chills, fatigue, anorexia, nausea
5) Tachypnea, tachycardia, hypotension
6) Leukocytosis

Question 6

Clinical presentation & Diagnosis - Physical examination

Answer 6

1) Diminished breath sounds over affected area

2) Inspiratory crackles during lung expansion

Question 7

Clinical presentation & Diagnosis - Radiography

1) Indication
2) Types of radiographic tests
3) Radiographic findings indicating pneumonia

Answer 7

Indication:
Carried out if suspect pneumonia, based on S/Sx, PE

Types:

1) Chest X-ray
- 1st line
2) CT scan
- Higher resolution but more expensive
- Reserved for patients who don’t respond to treatment / immunocompromised (consider non-bacterial causes of pneumonia)

Radiographic findings indicating pneumonia:

1) Dense consolidations
2) New/Progressive infiltrates

Question 8

Clinical presentation & Diagnosis - Lab tests

1) Lab findings
2) Clinical practice

Answer 8

Lab findings

1) Elevated CRP
2) Elevated procalcitonin

Clinical practice:
NOT recommended for routine use to guide antibiotic initiation / treatment
- Non-specific, limited discriminatory potential (will be elevated in other types of infection/inflammation)

Question 9

Clinical presentation & Diagnosis - Urinary antigen tests

1) How it works
2) Types of tests available
3) Limitations
4) Clinical practice

Answer 9

How it works:
Bacteria produces specific antigens that are secreted in urine –> can be detected using test

Types of tests available:
Tests available for:
1) S. pneumoniae
2) Legionella pneumophilia (serotype 1 only)

Limitations:

1) Only indicates exposure to bacteria –> unable to confirm if bacteria is causing an infection
2) Remains positive days-weeks even after antibiotic treatment

Clinical practice
- Not routinely used

Question 10

Cultures

1) Types of cultures
2) Use of cultures in treating pneumonia

Answer 10

Respiratory cultures:

1) Sputum
- Limitation: Low yield due to frequent contamination by oropharyngeal secretions
- Sample is considered of good quality if: (1) > 10 neutrophils AND (2) < 25 epithelial cells per low power field
- Will usually send sputum sample in most cases
2) Lower respiratory tract sample
- E.g. Bronchoalveolar lavage (BAL)
- Limitations: Invasive
- Advantages: Less contamination
- Clinical practice: Not frequently done; May be done for ICU patients, where high quality samples are important

Blood cultures
- Test for bacteremia

Use of cultures in treating pneumonia:

• Always send cultures (before antibiotic treatment if possible)
• May or may not be able to identify bacteria causing infection (sputum cultures have low yield) –> many pneumonia cases treated empirically
• Always initiate antibiotic treatment with clinical suspicion (i.e. S/Sx, PE, radiography) –> no need to confirm with cultures

Question 11

Classification of pneumonia

Answer 11

Nosocomial pneumonia:

1) Hospital-acquired pneumonia (HAP): Onset ≥ 48h after hospital admission
2) Ventilator-associated pneumonia (VAP): Onset ≥ 48h after mechanical ventilation

Community-acquired pneumonia:
Onset in community OR < 48h after hospital admission