What are the IDSA (Infectious Diseases Society of America)/ATS (American Thoracic Society) guidelines for the management of community-acquired pneumonia (CAP)?

IDSA/ATS Guidelines for Community-Acquired Pneumonia

Severity Assessment and Site of Care

Use a systematic approach to determine treatment location: assess for conditions compromising home safety, calculate the Pneumonia Severity Index (PSI) or CURB-65 score, then apply clinical judgment. 1, 2

• PSI risk classes I-III can be treated at home 2
• CURB-65 score of 0-1 without hypoxemia indicates outpatient candidacy 1, 3
• Patients requiring ICU admission should meet criteria for severe CAP (septic shock requiring vasopressors or respiratory failure requiring mechanical ventilation) 1

Empiric Antibiotic Therapy

Outpatient Treatment (Previously Healthy, No Recent Antibiotics)

For outpatient CAP, use amoxicillin 1g three times daily OR doxycycline 100mg twice daily as first-line therapy. 1, 2

• Alternative: macrolide monotherapy (azithromycin or clarithromycin) in regions with <25% high-level macrolide-resistant S. pneumoniae 1
• In regions with ≥25% macrolide resistance, avoid macrolide monotherapy 1

Outpatient Treatment (With Comorbidities or Recent Antibiotic Use)

Use a respiratory fluoroquinolone (moxifloxacin, gemifloxacin, or levofloxacin 750mg) OR combination therapy with high-dose amoxicillin (1g three times daily) or amoxicillin-clavulanate (2g twice daily) plus a macrolide. 1

• Alternative β-lactams: ceftriaxone, cefpodoxime, or cefuroxime 500mg twice daily 1
• Doxycycline is an acceptable alternative to macrolides 1

Inpatient Non-ICU Treatment

Hospitalized patients should receive either a respiratory fluoroquinolone alone OR a β-lactam (cefotaxime, ceftriaxone, or ampicillin) plus a macrolide. 1, 2

• Ertapenem is acceptable for patients with risk factors for gram-negative pathogens (excluding Pseudomonas) 1
• Doxycycline is an alternative to macrolides 1
• For penicillin-allergic patients, use a respiratory fluoroquinolone 1

Inpatient ICU Treatment

Severe CAP requires combination therapy with a β-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) PLUS either azithromycin OR a respiratory fluoroquinolone. 1, 2

For Pseudomonas risk factors (structural lung disease, severe COPD, recent broad-spectrum antibiotics), use an antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) plus either ciprofloxacin or levofloxacin 750mg. 1, 4

• Alternative for Pseudomonas coverage: antipseudomonal β-lactam plus aminoglycoside plus either azithromycin or antipneumococcal fluoroquinolone 1
• For suspected community-acquired MRSA, add vancomycin or linezolid 1, 2
• For penicillin allergy with Pseudomonas risk, substitute aztreonam for β-lactam 1

Timing and Administration

Administer the first antibiotic dose while the patient is still in the emergency department. 1, 2

• Initiate empiric therapy regardless of initial procalcitonin level 2
• Early treatment within 48 hours of symptom onset improves outcomes 1, 2

Transition to Oral Therapy

Switch from IV to oral antibiotics when the patient is hemodynamically stable, clinically improving, afebrile, able to ingest medications, and has normal GI function. 1

• Inpatient observation while receiving oral therapy is unnecessary 1
• Discharge as soon as clinically stable with no other active medical problems 1

Duration of Therapy

Treat for a minimum of 5 days, ensuring the patient is afebrile for 48-72 hours and has no more than one sign of clinical instability before stopping antibiotics. 1, 2, 5

• Longer duration (14-21 days) required for Legionella, S. aureus, or gram-negative enteric bacilli 5
• Extended therapy needed if initial antibiotics were inactive against the identified pathogen or if extrapulmonary complications exist (meningitis, endocarditis) 1

Pathogen-Directed Therapy

Once a pathogen is identified by reliable microbiological methods, narrow therapy to target that specific organism. 1, 2

Management of Treatment Failure

Reassess patients who fail to improve at 48-72 hours using a systematic classification based on timing and type of failure. 1

• Up to 15% of CAP patients do not respond appropriately to initial therapy 1
• Review clinical history, examination, prescription records, and all investigations 5

Supportive Care for Severe CAP

Use noninvasive ventilation for hypoxemia or respiratory distress unless immediate intubation is required (PaO₂/FiO₂ <150 with bilateral infiltrates). 1, 2

For mechanically ventilated patients with diffuse bilateral pneumonia or ARDS, use low-tidal-volume ventilation (6 mL/kg ideal body weight). 1, 2

• Screen hypotensive, fluid-resuscitated patients for occult adrenal insufficiency 1

Follow-Up

Arrange clinical review at 6 weeks with either the general practitioner or hospital clinic. 2, 5

• Obtain chest radiograph at follow-up for patients with persistent symptoms, physical signs, or higher malignancy risk (smokers, age >50 years) 2

Prevention

Administer pneumococcal polysaccharide vaccine to persons ≥65 years and those with high-risk conditions per ACIP guidelines. 1

Healthcare workers should receive annual influenza immunization. 1

• Assess vaccination status at hospital admission for all patients 1
• Vaccinate at discharge or during outpatient treatment 1