What is the recommended community‑acquired pneumonia (CAP) treatment protocol based on severity assessment using CURB‑65 (confusion, urea, respiratory rate, blood pressure, age ≥ 65) or Pneumonia Severity Index (PSI), including outpatient low‑risk, outpatient with comorbidities, inpatient non‑ICU, and ICU regimens?

Community-Acquired Pneumonia Treatment Protocol

Use CURB-65 as your primary severity assessment tool to guide site-of-care decisions for all adult CAP patients, with scores 0-1 treated outpatient, score 2 requiring clinical judgment for possible hospitalization, and scores ≥3 mandating hospital admission with immediate ICU evaluation using IDSA/ATS severe CAP criteria. 1, 2

Initial Severity Assessment with CURB-65

CURB-65 assigns one point for each of the following criteria 1, 2:

• Confusion (new-onset disorientation to person, place, or time)
• Urea >19 mg/dL (or BUN >20 mg/dL, or 7 mmol/L)
• Respiratory rate ≥30 breaths/minute
• Blood pressure: systolic <90 mmHg or diastolic ≤60 mmHg
• Age ≥65 years

Mortality Risk by Score 1, 2, 3:

• Score 0: 0.7% mortality
• Score 1: 2.1% mortality
• Score 2: 9.2% mortality
• Score 3: 14.5% mortality
• Score 4: 40% mortality
• Score 5: 57% mortality

Treatment Protocol by Risk Category

Low-Risk Outpatient (CURB-65 Score 0-1)

For previously healthy adults without comorbidities, use monotherapy 3:

• Amoxicillin 1g three times daily, OR
• Doxycycline 100mg twice daily

For adults with comorbidities (chronic heart/lung/liver/renal disease, diabetes, alcoholism, malignancy, asplenia), use combination therapy 3:

• Amoxicillin-clavulanate PLUS macrolide (azithromycin or clarithromycin), OR
• Cephalosporin (cefuroxime or cefpodoxime) PLUS macrolide

Expect clinical improvement within 3 days; patients must contact their physician if no improvement occurs 3.

Intermediate-Risk (CURB-65 Score 2)

This score carries 9.2% mortality and requires hospitalization or intensive in-home health services where available. 1, 2 Clinical judgment becomes critical at this threshold 3.

Factors that mandate admission despite score 2 2, 3:

• Inability to maintain oral intake
• Homelessness or lack of social support
• Active substance abuse or severe psychiatric illness
• Cognitive impairment affecting self-care
• Failure of prior outpatient antibiotic therapy
• Acute exacerbation of underlying comorbidities (COPD, heart failure)
• Prior splenectomy

High-Risk Inpatient Non-ICU (CURB-65 Score ≥3 without ICU criteria)

All patients with CURB-65 ≥3 require hospital admission and immediate evaluation for ICU placement. 1, 2 However, CURB-65 alone performs poorly for ICU triage decisions (sensitivity only 78.4%) 2, so you must apply IDSA/ATS severe CAP criteria.

ICU Admission Criteria (IDSA/ATS Severe CAP)

Direct ICU admission is mandatory for patients meeting either major criterion 1, 2:

Major Criteria (any one requires ICU):

• Septic shock requiring vasopressors
• Acute respiratory failure requiring intubation and mechanical ventilation

Minor Criteria (≥3 require ICU or high-level monitoring unit) 1, 2:

• Respiratory rate ≥30 breaths/minute
• PaO₂/FiO₂ ratio ≤250
• Multilobar infiltrates on chest imaging
• Confusion/disorientation
• Blood urea nitrogen ≥20 mg/dL
• Leukopenia (WBC <4,000 cells/mm³) from infection
• Thrombocytopenia (platelets <100,000/mm³)
• Hypothermia (core temperature <36°C)
• Hypotension requiring aggressive fluid resuscitation

Delayed ICU transfer (ward→ICU) is associated with significantly higher mortality, so evaluate ICU criteria immediately upon admission for all CURB-65 ≥3 patients. 1, 2

Alternative: Pneumonia Severity Index (PSI)

The PSI incorporates 20 variables and provides more granular risk stratification but is complex for emergency settings 1, 4. Use PSI when CURB-65 score is borderline (score 2) and you need additional detail to refine disposition decisions. 2

PSI Risk Classes 1, 4:

• Class I-II (mortality ≤0.7%): Outpatient treatment
• Class III (mortality 0.9-2.8%): Observation unit or short hospitalization
• Class IV (mortality 8%): Hospitalization required
• Class V (mortality 35%): Hospitalization required, high ICU risk

The PSI classifies slightly more patients as low-risk compared to CURB-65, but recent evidence shows CURB-65 is associated with lower 30-day mortality (8.6% vs 9.7%) and is more user-friendly. 1, 5

Critical Pitfalls to Avoid

Young patients (<65 years) with severe respiratory failure: CURB-65 may dangerously underestimate severity because age is heavily weighted; a 30-year-old with severe hypoxemia requiring high-flow oxygen scores only 0-2 points despite critical illness. 2, 3 Always assess oxygenation and work of breathing independently.

Elderly patients with stable comorbidities: A healthy 70-year-old with isolated tachypnea may score 2 points (age + respiratory rate) without true severe illness. 1, 2 Consider PSI or clinical gestalt in this scenario.

COPD patients: These patients have higher mechanical ventilation rates and ICU mortality when admitted with CAP, yet COPD is not captured in CURB-65 scoring. 1 Maintain lower threshold for admission.

For ICU decisions, never rely on CURB-65 alone—it has poor sensitivity for predicting need for critical care interventions. 2, 6 Always apply the IDSA/ATS severe CAP criteria systematically.

Simplified Alternative: CRB-65

When laboratory testing is unavailable (primary care office, resource-limited settings), use CRB-65, which omits the urea measurement and scores 0-4 points. 1, 2, 3 The same thresholds apply: 0-1 for outpatient, ≥2 for hospitalization consideration.