Community-Acquired Pneumonia: Diagnostic and Treatment Approach
Diagnosis
Diagnose CAP based on clinical signs/symptoms plus radiographic confirmation—chest X-ray remains the standard for confirming pneumonia, though clinical diagnosis alone is acceptable in mild outpatient cases. 1
Clinical Presentation
High-value clinical findings that increase CAP probability:
Absence of abnormal vital signs significantly decreases CAP probability (LR- = 0.25). 2
Radiographic Confirmation
- Chest radiography showing air space density is required for definitive diagnosis in hospitalized patients. 1, 3
- In mild outpatient CAP, clinical diagnosis without imaging is acceptable when radiographs are unavailable, though this introduces diagnostic uncertainty 4
- Lung ultrasound or CT can substitute when chest X-ray is unavailable 5
Microbiological Testing
Do NOT obtain routine sputum cultures or blood cultures in outpatients—reserve these for specific high-risk situations only. 1
Outpatient Setting:
- No sputum Gram stain/culture (strong recommendation) 1
- No blood cultures (strong recommendation) 1
- No routine urine antigen testing for pneumococcus or Legionella 1
Hospitalized Non-Severe CAP:
- Do NOT routinely obtain sputum or blood cultures (conditional recommendation) 1
- Testing yields are poor and do not improve individual patient outcomes 1
Severe CAP or High-Risk Patients—OBTAIN CULTURES:
Obtain pretreatment sputum cultures, blood cultures, and urine antigens when patients have: 1
- Severe CAP (septic shock requiring vasopressors OR respiratory failure requiring mechanical ventilation) 1
- Empiric treatment planned for MRSA or Pseudomonas aeruginosa 1
- Prior infection with MRSA or P. aeruginosa 1
- Hospitalization with IV antibiotics in last 90 days 1
For severe CAP specifically, also obtain: 1
- Legionella urinary antigen 1
- Respiratory secretions for Legionella culture or nucleic acid testing 1
- Pneumococcal urinary antigen 1
Viral Testing
- Test ALL patients for COVID-19 and influenza when these viruses are circulating in the community—results directly affect treatment decisions and infection control 3
Biomarkers
- Do NOT use procalcitonin to determine need for initial antibacterial therapy 1, 5
- Procalcitonin, CRP, and WBC are not specific enough for bacterial vs. viral differentiation 6
Severity Assessment and Site of Care
Use validated severity scores (PSI or CURB-65) to determine hospitalization need and treatment intensity. 1, 7
CURB-65 Scoring (preferred in primary care—no labs required): 5
- Confusion
- Urea (BUN >19 mg/dL)
- Respiratory rate ≥30/min
- Blood pressure (systolic <90 or diastolic ≤60 mmHg)
- Age ≥65 years
Severe CAP Criteria (requires ICU consideration): 1
- Septic shock requiring vasopressors
- Respiratory failure requiring mechanical ventilation
Empiric Antibiotic Treatment
Initiate empiric antibiotics immediately based on severity and risk factors—do NOT delay for diagnostic testing. 1, 7, 3
Outpatient Treatment
Healthy Adults WITHOUT Comorbidities:
First-line monotherapy options: 7, 5
- Amoxicillin (preferred)
- Doxycycline
- Macrolide (azithromycin or clarithromycin)—ONLY if local pneumococcal macrolide resistance <25% 1, 5
Note: Macrolide monotherapy is now a conditional (not strong) recommendation due to rising resistance 1
Adults WITH Comorbidities (COPD, diabetes, heart/liver/renal disease):
Combination therapy or fluoroquinolone monotherapy: 7, 5
- Amoxicillin-clavulanate PLUS macrolide (azithromycin or clarithromycin), OR
- Amoxicillin-clavulanate PLUS doxycycline, OR
- Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin) 7, 8
Hospitalized Non-Severe CAP
β-lactam PLUS macrolide combination is preferred over β-lactam plus fluoroquinolone based on stronger evidence: 1, 3
- Ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg daily (preferred) 3
- Alternative: Cefotaxime or β-lactam/β-lactamase inhibitor PLUS macrolide 1
- Alternative: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily) 1, 8
Severe CAP (ICU Patients)
β-lactam PLUS macrolide combination has stronger evidence than β-lactam plus fluoroquinolone: 1
- Ceftriaxone 2 g IV daily PLUS azithromycin 500 mg daily, OR
- Cefotaxime or β-lactam/β-lactamase inhibitor PLUS macrolide 1
- Alternative: β-lactam PLUS respiratory fluoroquinolone 1
Add MRSA coverage (vancomycin or linezolid) if: 1
- Prior MRSA infection
- IV antibiotics in last 90 days
- High local MRSA prevalence
Add Pseudomonas coverage (piperacillin-tazobactam, cefepime, or meropenem) if: 1
- Prior Pseudomonas infection
- Structural lung disease (bronchiectasis)
- Recent hospitalization with IV antibiotics
Treatment Duration and Follow-Up
Minimum 5 days of therapy for all patients, with clinical stability required before discontinuation: 7
- Patient must be afebrile for 48-72 hours 7
- No more than one CAP-associated sign of clinical instability 7
Reassess at 48-72 hours: 7
- Evaluate clinical response
- De-escalate therapy if pathogen identified and susceptibilities known 7
- Consider treatment failure if no improvement
Corticosteroids
Do NOT routinely use corticosteroids, EXCEPT: 1
- May consider in refractory septic shock 1
- Systemic corticosteroids within 24 hours of severe CAP development may reduce 28-day mortality 3
Follow-Up Imaging
Do NOT obtain routine follow-up chest radiographs in patients who achieve clinical stability. 1
- Consider lung cancer screening if patient meets eligibility criteria 1
Key Pitfalls to Avoid
- Abandoning "healthcare-associated pneumonia" (HCAP) category: Do not automatically treat all nursing home residents or recently hospitalized patients for resistant pathogens—use validated individual risk factors instead 1
- Over-reliance on clinical features alone: Cannot reliably distinguish bacterial from viral or typical from atypical pathogens 9
- Obtaining cultures in low-risk patients: Up to 50% of CAP cases have no pathogen identified even with extensive testing—empiric therapy is appropriate 9
- Delaying antibiotics for test results: Initiate empiric therapy immediately; outcomes improve with early treatment 3