What is the workup, diagnostic scoring tool, and treatment for community-acquired pneumonia (CAP) in the inpatient setting?

Community-Acquired Pneumonia Workup and Inpatient Treatment

Diagnostic Workup

For hospitalized patients with CAP, obtain pretreatment blood cultures and expectorated sputum for Gram stain and culture if the patient has any of the following clinical indications: ICU admission, failure of outpatient therapy, cavitary infiltrates, leukopenia, active alcohol abuse, severe obstructive/structural lung disease, asplenia, positive pneumococcal or Legionella urinary antigen, or pleural effusion. 1

Essential Tests for All Inpatients

• Blood cultures (two sets) prior to antibiotic administration 1
• Chest radiograph to confirm pneumonia and assess severity 1
• Pulse oximetry or arterial blood gas if oxygen saturation <90% or respiratory distress 1
• Complete blood count with differential 1
• Basic metabolic panel including blood urea nitrogen and creatinine 1

Additional Tests for Severe CAP (ICU Patients)

• Expectorated sputum Gram stain and culture (or endotracheal aspirate if intubated) 1
• Urinary antigen tests for Legionella pneumophila and Streptococcus pneumoniae 1
• Procalcitonin may help limit antibiotic overuse, though empiric therapy should not be delayed 1

Sputum Collection Standards

Only process sputum samples that meet quality criteria: <10 squamous epithelial cells and >25 polymorphonuclear leukocytes per low-power field, with proper collection, transport, and processing protocols in place. 1

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Severity Assessment Tool

Use the 2007 IDSA/ATS severe CAP criteria to determine ICU admission need, as these criteria are more accurate than PSI or CURB-65 for identifying patients requiring intensive care. 1

IDSA/ATS Severe CAP Criteria (ICU Admission if ≥1 Major or ≥3 Minor)

Major Criteria:

• Septic shock requiring vasopressors 1
• Respiratory failure requiring mechanical ventilation 1

Minor Criteria:

• Respiratory rate ≥30 breaths/min 1
• PaO₂/FiO₂ ratio ≤250 1
• Multilobar infiltrates 1
• Confusion/disorientation 1
• Uremia (BUN ≥20 mg/dL) 1
• Leukopenia (WBC <4,000 cells/mm³) 1
• Thrombocytopenia (platelets <100,000/mm³) 1
• Hypothermia (core temperature <36°C) 1
• Hypotension requiring aggressive fluid resuscitation 1

For General Admission Decisions

Use the Pneumonia Severity Index (PSI) as an adjunct to clinical judgment for determining whether outpatient versus inpatient treatment is appropriate, as it effectively identifies low-risk patients (PSI classes I-III with ≤3% mortality) who can be safely treated at home. 1

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Inpatient Antibiotic Treatment

Non-ICU Hospitalized Patients

Administer a β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS a macrolide (azithromycin or clarithromycin), OR use respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin 400 mg daily). 1, 2

Specific regimens:

• Preferred combination: Ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg IV/PO daily 1, 3
• Alternative combination: Ampicillin-sulbactam 1.5-3 g IV every 6 hours PLUS azithromycin 500 mg IV/PO daily 1
• Monotherapy option: Levofloxacin 750 mg IV/PO daily 1
• For penicillin allergy: Respiratory fluoroquinolone plus aztreonam 1

ICU Patients (Severe CAP)

Treat with a β-lactam (ceftriaxone, cefotaxime, or ampicillin-sulbactam) PLUS either azithromycin OR a respiratory fluoroquinolone—combination therapy is mandatory for severe CAP. 1

Standard severe CAP regimen:

• Ceftriaxone 1-2 g IV daily (or cefotaxime 1-2 g IV every 8 hours) PLUS azithromycin 500 mg IV daily 1
• Alternative: β-lactam PLUS levofloxacin 750 mg IV daily 1

Special Pathogen Coverage

For Pseudomonas aeruginosa risk factors (prior P. aeruginosa isolation, structural lung disease like bronchiectasis):

• Antipseudomonal β-lactam (piperacillin-tazobactam 4.5 g IV every 6 hours, cefepime 2 g IV every 8 hours, imipenem, or meropenem) PLUS ciprofloxacin 400 mg IV every 8-12 hours OR levofloxacin 750 mg IV daily 1
• Alternative: Antipseudomonal β-lactam PLUS aminoglycoside PLUS azithromycin or respiratory fluoroquinolone 1

For community-acquired MRSA (post-influenza pneumonia, necrotizing pneumonia, cavitation):

• Add vancomycin 15-20 mg/kg IV every 8-12 hours OR linezolid 600 mg IV every 12 hours to standard regimen 1

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Timing and Duration

Administer the first antibiotic dose in the emergency department before hospital admission to minimize time to treatment. 1

Treat for a minimum of 5 days once the patient achieves clinical stability (temperature ≤37.8°C, heart rate ≤100 bpm, respiratory rate ≤24 breaths/min, systolic blood pressure ≥90 mmHg, oxygen saturation ≥90%, ability to eat, normal mentation). 1, 4, 2

For S. aureus or P. aeruginosa, extend treatment to 7 days minimum. 4

For Legionella, extend treatment to 14 days. 2

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IV to Oral Conversion

Switch from IV to oral antibiotics when the patient is hemodynamically stable, improving clinically (decreased cough/dyspnea), afebrile for 12-24 hours, has decreasing white blood cell count, and can tolerate oral intake. 2, 5

Use the same antibiotic class when switching (e.g., IV ceftriaxone → oral cefpodoxime; IV azithromycin → oral azithromycin; IV levofloxacin → oral levofloxacin). 4

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Common Pitfalls

Avoid using macrolide monotherapy in regions with >25% macrolide-resistant S. pneumoniae. 1

Do not empirically cover MRSA or Pseudomonas without validated risk factors—the healthcare-associated pneumonia (HCAP) classification should be abandoned. 1, 4

Obtain blood and sputum cultures BEFORE starting antibiotics in severe CAP—positive cultures guide de-escalation and narrow-spectrum therapy within 48-72 hours. 1

Reassess patients who fail to achieve clinical stability within 72 hours—consider resistant pathogens, complications (empyema, lung abscess), alternative diagnoses, or non-infectious mimics. 2