Community-Acquired Pneumonia (CAP)

CAP Summary

Definition

  • Infection of lung tissue acquired outside hospital
  • Air sacs filled with microorganisms/fluid
  • Affects lung function

Common Causes

  • Bacterial: S. pneumoniae (most common)
  • Viral: Influenza, RSV
  • Atypical: Mycoplasma, Legionella

Clinical Features

  • Cough, dyspnea, sputum production
  • Fever, chills, pleural pain
  • Tachypnea, tachycardia, hypoxia
  • Focal chest signs

CURB-65 Score

  • 0-1: Low severity (outpatient)
  • 2: Moderate (hospital admission)
  • 3-5: High severity (urgent admission)

Antibiotic Therapy

  • Low severity: Amoxicillin 5d
  • Moderate: Amoxicillin + Clarithromycin
  • High: Co-amoxiclav + Clarithromycin

Red Flags

  • Start antibiotics within 4h (1h if sepsis)
  • Oxygen to maintain SpO₂ 94-98%
  • Confusion (especially elderly)
  • Hypotension, tachypnea ≥30

Pediatric CAP

  • Viral most common <1 year
  • Fever >39°C, tachypnea
  • Non-severe: Amoxicillin
  • Severe: Co-amoxiclav ± Macrolide

Community-Acquired Pneumonia (CAP)

Definition

Pneumonia is an infection of the lung tissue in which the air sacs become filled with microorganisms, fluid and inflammatory cells, affecting lung function. CAP is acquired outside of hospital.

Causes

Bacterial

  • Streptococcus pneumoniae (most common)
  • Haemophilus influenzae
  • Staphylococcus aureus
  • Klebsiella spp.
  • Moraxella catarrhalis

Viral

  • Influenza A and B
  • Respiratory syncytial virus (RSV)
  • Adenovirus
  • Coronavirus

Atypical Organisms

  • Mycoplasma pneumoniae
  • Chlamydia pneumoniae
  • Legionella pneumophila
  • Coxiella burnetii

Clinical Features

History

  • Cough
  • Dyspnea
  • Sputum production
  • Pleural pain
  • Fever, chills, myalgia

Examination

  • Tachypnea, tachycardia
  • Fever (>38°C)
  • Focal chest signs:
    • Decreased breath sounds
    • Bronchial breath sounds
    • Coarse crepitations
    • Dullness to percussion
  • Hypoxia
  • Confusion (especially elderly)

Red Flags for Atypical Pathogens

Legionella
  • Dry cough
  • Headache
  • Confusion
  • Diarrhea
  • Hyponatremia
Mycoplasma
  • Upper respiratory symptoms
  • Rash
  • Encephalitis
  • Hemolytic anemia

Investigations

Essential

  • Pulse oximetry
  • CXR (consolidation ± effusion)
  • FBC, U&Es, CRP, LFTs
  • ABG if SpO₂ <92%

Microbiology (Moderate/Severe CAP)

  • Blood cultures
  • Sputum culture/Gram stain
  • Urine antigens (if atypical suspected)
  • PCR/serology if atypical pathogens

Severity Assessment (CURB-65)

Feature Criteria Points
Confusion AMTS ≤8 or new disorientation 1
Urea >7 mmol/L 1
Respiratory rate ≥30 breaths/min 1
Blood pressure SBP <90 or DBP ≤60 mmHg 1
Age ≥65 years 1

Score 0-1

  • Low severity (<3% mortality)
  • Consider outpatient treatment

Score 2

  • Moderate severity (3-15% mortality)
  • Consider hospital admission

Score 3-5

  • High severity (>15% mortality)
  • Urgent hospital admission
  • Consider ICU assessment

Management

General Measures

  • Start antibiotics within 4 hours (1 hour if sepsis)
  • Oxygen to maintain SpO₂ 94-98% (88-92% if COPD)
  • Analgesia for pleuritic pain
  • IV fluids if dehydrated
  • VTE prophylaxis if immobile
  • Nutritional support if prolonged illness

Antibiotic Therapy

Severity First Choice Alternatives
Low Amoxicillin 500mg TDS (5d) Doxycycline, Clarithromycin, Erythromycin (penicillin allergy/atypical)
Moderate Amoxicillin + Clarithromycin (if atypical) Doxycycline or Clarithromycin (penicillin allergy)
High Co-amoxiclav + Clarithromycin Levofloxacin (penicillin allergy)

Complications

Pulmonary

  • Pleural effusion/empyema
  • Lung abscess
  • ARDS
  • Necrotizing pneumonia
  • Pneumothorax

Systemic

  • Septic shock
  • Disseminated infection
  • Postinfectious bronchiectasis

Pediatric CAP

Causes

  • Viral (most common <1yr): RSV, influenza
  • Bacterial: S. pneumoniae, H. influenzae, S. aureus
  • Older children: Mycoplasma, Chlamydia

Clinical Features

  • Fever >39°C
  • Tachypnea (age-dependent)
  • Chest indrawing/nasal flaring
  • Focal crackles
  • SpO₂ ≤95%

Management

  • Non-severe: Amoxicillin
  • Severe: Co-amoxiclav ± Macrolide
  • Oxygen if SpO₂ <92%
  • Refer neonates to specialist