Community-acquired pneumonia

Quick Overview

Community-acquired pneumonia (CAP) is acute lower respiratory tract infection acquired outside hospital, affecting lung parenchyma. NICE NG138 emphasises structured severity assessment using CURB-65 to guide antibiotic choice and admission decisions. Mortality ranges from <1% (low severity) to 15-40% (high severity), making accurate risk stratification critical.

Core Facts & Concepts

CURB-65 Severity Score (1 point each):

• Confusion (AMT ≤8 or new disorientation)
• Urea >7 mmol/L
• Respiratory rate ≥30/min
• Blood pressure: SBP <90 mmHg or DBP ≤60 mmHg
• Age ≥65 years

Management Thresholds:

• Score 0-1: Low severity → consider home treatment
• Score 2: Moderate severity → consider hospital admission
• Score 3-5: High severity → urgent hospital admission (ICU if score 4-5)

Antibiotic Choices (NICE NG138):

📊 Key Numbers:

• Response expected within 48-72 hours
• CRP >100 mg/L suggests bacterial (not viral) aetiology
• Repeat CXR at 6 weeks if >50 years or smoker (exclude malignancy)

Problem-Solving Approach

Step-by-Step Assessment:

1. Confirm diagnosis: Cough + ≥1 symptom (fever, pleuritic pain, dyspnoea) + focal chest signs or systemic features
2. Calculate CURB-65 (requires vital signs, blood tests, cognitive assessment)
3. Order investigations:
   • Bloods: FBC, U&E, CRP, LFTs
   • CXR (diagnostic but don't delay antibiotics)
   • Sputum/blood cultures before antibiotics if moderate-high severity
4. Decide location: Home vs ward vs ICU
5. Start antibiotics within 4 hours of hospital presentation (sepsis pathway if shocked)

🚩 Red Flags for ICU Admission:

• CURB-65 ≥4
• Hypoxia requiring >60% FiO₂
• Bilateral/multilobar involvement
• Septic shock (lactate >2, vasopressor need)

When to Consider Atypical Cover:

• No response to β-lactam after 48 hours
• Legionella risk (travel, outbreak, hyponatraemia)
• Mycoplasma/Chlamydia suspected (dry cough, extrapulmonary features)
• Moderate-high severity (dual therapy standard)

⚠️ Warning: Penicillin allergy → use doxycycline 200mg stat then 100mg OD (covers typical + atypical)

Analysis Framework

Differentials to Exclude:

Admission vs Discharge Criteria:

Admit if:

• CURB-65 ≥2
• Hypoxia (SpO₂ <90% on air)
• Social concerns (unable to cope at home)
• Co-morbidities decompensating

Discharge if:

• CURB-65 0-1 + SpO₂ >90% + tolerating oral + safe home environment

Visual Aid

Antibiotic Allergy Alternatives:

Key Points Summary

✓ CURB-65 drives all decisions: 0-1 home, 2 consider admission, 3-5 urgent admission (calculate from Confusion, Urea >7, RR ≥30, BP low, age ≥65)

✓ Antibiotic timing matters: Start within 4 hours if admitted; don't delay for investigations

✓ Low severity = amoxicillin monotherapy (500mg TDS × 5 days); moderate-high severity = dual therapy with macrolide for atypical cover

✓ Follow-up CXR at 6 weeks mandatory if >50 years or smoker (exclude underlying malignancy)

✓ 48-72 hour review critical: If no response, consider atypical pathogens, complications (empyema, abscess), or alternative diagnosis

✓ Penicillin allergy: Use doxycycline (covers typical + atypical); avoid quinolones unless severe allergy

✓ ICU criteria: CURB-65 ≥4, severe hypoxia, bilateral involvement, or septic shock requiring vasopressors

📌 Remember: CURB-65 - Confusion, Urea >7, RR ≥30, BP low (SBP <90), 65 years old