What is the recommended approach to treating community-acquired pneumonia in a typical adult patient with consideration of age, underlying health conditions, and immunization status?

Approach to Community-Acquired Pneumonia in Adults

Initial Assessment and Risk Stratification

Use the CRB-65 score (confusion, respiratory rate ≥30, blood pressure <90/60, age ≥65) to determine site of care: score 0 = outpatient, score 1-2 = consider hospitalization, score ≥3 = hospitalize with ICU consideration. 1

• Obtain chest radiograph, lung ultrasound, or CT to confirm air space density consistent with pneumonia 2, 1
• Test for COVID-19 and influenza when these viruses are circulating in the community, as results directly affect treatment decisions 2
• Assess for immunosuppression (18% of hospitalized CAP patients have immunocompromising conditions), as this population requires broader empirical coverage 3, 4
• Evaluate for risk factors indicating resistant pathogens: structural lung disease, recent hospitalization with IV antibiotics within 90 days, prior isolation of Pseudomonas aeruginosa or MRSA 5, 6

Microbiological Testing

For hospitalized patients, obtain blood cultures and sputum Gram stain/culture before initiating antibiotics to enable pathogen-directed therapy. 5

• Recognize that only 38% of hospitalized CAP patients have a pathogen identified: viruses in 40% of those with identified etiology, Streptococcus pneumoniae in 15% 2
• Consider urinary antigen testing for Legionella pneumophila serogroup 1 in severe CAP or ICU patients 5
• Do not use procalcitonin measurement for diagnosis 1

Empirical Antibiotic Therapy by Clinical Setting

Outpatient Treatment - Previously Healthy Adults Without Comorbidities

Prescribe amoxicillin 1 g orally three times daily for 5-7 days as first-line therapy. 5, 1

• Alternative: doxycycline 100 mg orally twice daily 5, 1
• Use macrolides (azithromycin 500 mg day 1, then 250 mg daily for days 2-5) only in areas where pneumococcal macrolide resistance is documented <25% 5, 1

Outpatient Treatment - Adults With Comorbidities

Prescribe combination therapy: amoxicillin-clavulanate 875/125 mg orally twice daily PLUS azithromycin 500 mg day 1, then 250 mg daily for days 2-5, for a total duration of 5-7 days. 5

• Alternative: respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) 5, 7
• Comorbidities include COPD, diabetes, chronic heart/liver/renal disease, malignancy, or antibiotic use within past 3 months 5

Hospitalized Non-ICU Patients

Administer ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg daily, starting immediately in the emergency department. 5, 6, 2

• Alternative: respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 5, 6
• For penicillin-allergic patients, use respiratory fluoroquinolone as preferred alternative 5
• Delayed antibiotic administration beyond 8 hours increases 30-day mortality by 20-30% 5, 6

Severe CAP Requiring ICU Admission

Administer mandatory combination therapy: ceftriaxone 2 g IV daily PLUS azithromycin 500 mg IV daily OR respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 5, 6, 2

• Monotherapy is inadequate for severe disease 5
• Consider systemic corticosteroids within 24 hours of severe CAP development to reduce 28-day mortality 2

Coverage for Resistant Pathogens

Pseudomonas aeruginosa Coverage

Add antipseudomonal coverage only when specific risk factors are present: structural lung disease, recent hospitalization with IV antibiotics within 90 days, or prior respiratory isolation of P. aeruginosa. 5, 6

• Regimen: antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin 400 mg IV every 8 hours OR levofloxacin 750 mg IV daily 5, 6

MRSA Coverage

Add vancomycin 15 mg/kg IV every 8-12 hours OR linezolid 600 mg IV every 12 hours only when specific risk factors are present: prior MRSA infection/colonization, recent hospitalization with IV antibiotics, post-influenza pneumonia, or cavitary infiltrates on imaging. 5, 6

Duration of Therapy and Transition to Oral Antibiotics

Treat for a minimum of 5 days and until the patient is afebrile for 48-72 hours with no more than one sign of clinical instability; typical duration for uncomplicated CAP is 5-7 days. 5, 6, 2

• Switch from IV to oral therapy when the patient is hemodynamically stable, clinically improving, able to take oral medications, and has normal GI function—typically by day 2-3 of hospitalization 5, 6
• Extend duration to 14-21 days for Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli 5, 6

Management of Treatment Failure

If no clinical improvement by day 2-3, obtain repeat chest radiograph, CRP, white cell count, and additional microbiological specimens. 8

• Consider chest CT to reveal unsuspected pleural effusions, lung abscess, or central airway obstruction 8, 6
• Perform thoracentesis whenever significant pleural fluid is present 8
• For non-severe pneumonia initially treated with amoxicillin monotherapy, add or substitute a macrolide 8
• For severe pneumonia not responding to combination therapy, consider adding rifampicin 8

Prevention Strategies

Assess vaccination status at hospital admission and administer pneumococcal polysaccharide vaccine to all patients ≥65 years and those with high-risk conditions. 8

• Administer 20-valent pneumococcal conjugate vaccine alone OR 15-valent pneumococcal conjugate vaccine followed by 23-valent pneumococcal polysaccharide vaccine one year later 8, 1
• Offer annual influenza vaccine to all patients, especially during fall and winter 8
• Make smoking cessation a goal for all patients hospitalized with CAP who smoke 8

Critical Pitfalls to Avoid

Never use macrolide monotherapy in hospitalized patients, as this provides inadequate coverage for typical bacterial pathogens like S. pneumoniae. 5

• Avoid macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25%, as this leads to treatment failure 5, 1
• Do not add antipseudomonal or MRSA coverage empirically without documented risk factors 5, 6
• Avoid extending therapy beyond 7-8 days in responding patients without specific indications, as this increases antimicrobial resistance risk 5
• Do not delay initial antibiotic administration—administer first dose in the emergency department 5, 6