Community-Acquired Pneumonia: Severity Scores, Antibiotics & Admission Criteria

A pragmatic ED-to-ward algorithm: diagnose CAP clinically with imaging support, risk-stratify, start timely empirics tailored to comorbidities and local resistance, and de-escalate as data clarifies—aiming for rapid recovery with minimal harm.

Recognition & Differentials

• Symptoms: fever, cough, purulent sputum, pleuritic chest pain, dyspnea.
• Exam: tachypnea, hypoxemia, crackles, bronchial breath sounds; pleural rub/effusion.
• Differentials: acute bronchitis, COPD/asthma exacerbation, PE, CHF, viral URI/influenza/COVID-19, aspiration pneumonitis, organizing pneumonia.

Initial Testing (do not delay antibiotics once CAP is likely)

• Imaging: CXR PA/lat; lung ultrasound can detect consolidations/B-lines/pleural effusions; CT only if uncertain/complicated.
• Labs: CBC, CMP, CRP/Procalcitonin (trend may help de-escalation, not initiation), blood gas if hypoxemic, lactate if septic.
• Micro: viral PCR (influenza/COVID-19, seasonal viruses), sputum culture if severe CAP, MRSA risk, or failure to improve; blood cultures for severe CAP or sepsis.
• ECG and troponin if chest pain/risk factors; complications and Type 2 MI occur.

Severity Scores → Disposition

• CURB-65: Confusion, Urea >7 mmol/L (20 mg/dL BUN), Respiratory rate ≥30, BP <90 systolic or ≤60 diastolic, Age ≥65.
  0–1: likely outpatient; 2: consider short stay/close follow-up; ≥3: admit (possible ICU).
• PSI/PORT: more granular mortality risk; higher classes favor admission.
• ICU triggers (any): need for mechanical ventilation or vasopressors; or ≥3 minor criteria (e.g., RR ≥30, PaO₂/FiO₂ ≤250, multilobar, confusion, BUN high, leukopenia, thrombocytopenia, hypothermia, hypotension requiring fluids).
• Always layer scores with clinical judgment, O₂ needs, social support, and comorbidity burden.

Empiric Antibiotics (adult)

Base choices on local resistance, allergies, QT/prolongation risks, and drug interactions. Reassess at 48–72 h.

Outpatient — no comorbidities or MRSA/Pseudomonas risk

• Amoxicillin high-dose or doxycycline.
• Macrolide monotherapy only where pneumococcal macrolide resistance is low per local data.

Outpatient — with comorbidities (chronic heart/lung/liver/renal disease; diabetes; alcoholism; malignancy; asplenia)

• Amoxicillin-clavulanate (or oral cephalosporin such as cefpodoxime/cefuroxime) plus macrolide or doxycycline,
• or respiratory fluoroquinolone monotherapy (levofloxacin/moxifloxacin) when appropriate risk-benefit.

Inpatient (non-ICU)

• IV beta-lactam (e.g., ceftriaxone, cefotaxime, or amp-sulbactam) plus azithromycin or doxycycline,
• or respiratory fluoroquinolone monotherapy.

Severe CAP (ICU) — no MRSA/Pseudomonas risk

• IV beta-lactam (ceftriaxone/cefotaxime/amp-sulbactam) plus azithromycin or a respiratory fluoroquinolone.

Add-on coverage when risk factors exist

• MRSA risk (post-influenza necrotizing pneumonia, prior MRSA, severe CAP with cavitation): add vancomycin or linezolid; de-escalate if cultures/PCR negative.
• Pseudomonas risk (structural lung disease, prior Pseudomonas, recent broad-spectrum antibiotics): antipseudomonal beta-lactam (e.g., piperacillin-tazobactam, cefepime) ± macrolide/fluoroquinolone per severity.
• Aspiration context: standard CAP regimens generally suffice; add anaerobic coverage only if lung abscess/empyema or classic aspiration syndromes.

Duration & IV→PO switch

• Minimum 5 days total therapy and clinically stable ≥48 h (afebrile, HR/RR improving, O₂ stable, oral intake adequate).
• Switch to oral once stable and GI absorption is reliable; complete the shortest effective duration.

Supportive Care

• Target SpO₂ ~92–96% (or baseline for chronic hypercapnia); consider high-flow/NIV if hypoxemic respiratory failure.
• Fluids for sepsis guided by perfusion; avoid overload in CHF/CKD.
• Antipyretics, incentive spirometry, early mobilization; VTE prophylaxis if admitted.
• Systemic steroids are not routine for typical CAP; consider only for refractory septic shock or specific conditions per protocol.

Reassessment & De-escalation (48–72 h)

• Review cultures, viral PCR, urinary antigens (pneumococcus/Legionella where used); narrow therapy accordingly.
• If no clinical response, re-evaluate diagnosis (PE, CHF, organizing pneumonia, resistant organisms, empyema/abscess) and consider CT/US and specialist input.

Discharge Planning

• Stable vitals on room air or home O₂ baseline, oral intake adequate, safe PO antibiotics plan, education on warning signs, and follow-up within 48–72 h (outpatient) or 1–2 weeks (post-admission).
• Vaccination review: influenza, pneumococcal series, COVID-19 per guidelines.
• Smoking cessation and pulmonary rehab referral when indicated.

Pearls & Pitfalls

• Don’t delay first antibiotic dose for “perfect” tests—draw cultures if needed and start therapy.
• Macrolide monotherapy only where resistance is low; otherwise pair or choose alternatives.
• Think viral in season—positive influenza/COVID-19 may change antibiotics and add antivirals.
• Beware silent hypoxemia in elderly; disposition is more than a score—assess supports and comorbidities.

Patient FAQs

“Why only five days of antibiotics?” Short, targeted courses work as well and reduce side effects and resistance—provided you’re clinically stable.

“Do I need a repeat X-ray?” If symptoms resolve, many patients don’t need one. Smokers >50 years or persistent symptoms often get a follow-up image at ~6 weeks to exclude hidden lesions.

References & Notes

Practical CAP pathway emphasizing early risk-stratification, appropriate empirics by setting/comorbidity, and timely de-escalation with a 5-day minimum once stable. Follow local antibiograms and institutional protocols. Educational only.