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

IDSA/ATS Guidelines for Community-Acquired Pneumonia

The 2019 IDSA/ATS guidelines provide the most current evidence-based recommendations for treating community-acquired pneumonia, with treatment stratified by severity and location of care, emphasizing combination β-lactam/macrolide therapy for hospitalized patients and shorter antibiotic durations than previously recommended. 1, 2

Outpatient Treatment

Healthy Adults Without Comorbidities

• Amoxicillin 1 g three times daily is the preferred first-line therapy for previously healthy adults, providing effective coverage against common CAP pathogens 2
• Doxycycline 100 mg twice daily serves as an acceptable alternative 2
• Macrolides (azithromycin 500 mg day 1, then 250 mg daily; or clarithromycin 500 mg twice daily) should only be used in areas where pneumococcal macrolide resistance is <25% 1, 2

Adults With Comorbidities

• Combination therapy with β-lactam (amoxicillin/clavulanate, cefpodoxime, or cefuroxime) plus macrolide (azithromycin or clarithromycin) or doxycycline is recommended 2
• Respiratory fluoroquinolone monotherapy (levofloxacin, moxifloxacin, or gemifloxacin) is equally effective 2

Inpatient Non-ICU Treatment

For hospitalized patients not requiring ICU admission, use either:

• β-lactam (ampicillin-sulbactam, cefotaxime, ceftriaxone, or ceftaroline) plus macrolide (strong recommendation, high quality evidence) 1, 2
• Respiratory fluoroquinolone monotherapy (levofloxacin or moxifloxacin) (strong recommendation, high quality evidence) 1, 2
• β-lactam plus doxycycline as an alternative (conditional recommendation, low quality evidence) 1, 2

Penicillin-Allergic Patients

• Use a respiratory fluoroquinolone for non-ICU patients 1, 2, 3

ICU Treatment

For severe CAP requiring ICU admission:

• β-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) plus either azithromycin (level II evidence) or fluoroquinolone (level I evidence) (strong recommendation) 1, 2
• The 2019 guidelines note stronger evidence favoring β-lactam/macrolide combination over β-lactam/fluoroquinolone for severe CAP 1

Penicillin-Allergic ICU Patients

• Respiratory fluoroquinolone plus aztreonam is recommended 1, 3

Coverage for Drug-Resistant Pathogens

Pseudomonas aeruginosa Coverage

Indicated for patients with:

• Structural lung disease (bronchiectasis)
• Recent hospitalization with parenteral antibiotics
• Prior respiratory isolation of P. aeruginosa
• Recent broad-spectrum antibiotic use 2

Regimen:

• Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) plus either ciprofloxacin or levofloxacin 750 mg 1
• Alternative: β-lactam plus aminoglycoside plus azithromycin or antipneumococcal fluoroquinolone 1
• For penicillin allergy: substitute aztreonam for β-lactam 1

MRSA Coverage

Indicated for patients with:

• Prior MRSA infection or colonization
• Recent hospitalization with parenteral antibiotics
• Cavitary infiltrates on imaging
• Concurrent influenza 2

Add vancomycin or linezolid to the base regimen (moderate recommendation, level III evidence) 1, 2

Diagnostic Testing Updates (2019 vs 2007)

The 2019 guidelines expanded indications for blood and sputum cultures beyond just severe disease:

• Now recommended for all inpatients empirically treated for MRSA or P. aeruginosa, in addition to patients with severe disease 1
• Urine pneumococcal antigen testing recommended for severe CAP 1
• Legionella urinary antigen testing recommended for severe CAP or when epidemiologically indicated (outbreak, recent travel) 1

Duration of Therapy

Treat for a minimum of 5 days (level I evidence), with patients meeting ALL of the following criteria before discontinuation:

• Afebrile for 48-72 hours
• No more than 1 CAP-associated sign of clinical instability 1, 2

Standard duration is 5-7 days for uncomplicated CAP 2

Longer duration needed if:

• Initial therapy was not active against identified pathogen
• Complicated by extrapulmonary infection (meningitis, endocarditis) 1

Transition to Oral Therapy

Switch from IV to oral therapy when patients are:

• Hemodynamically stable
• Clinically improving
• Able to ingest medications
• Have normally functioning gastrointestinal tract 1, 2

Discharge as soon as clinically stable with no other active medical problems and safe environment for continued care—inpatient observation while receiving oral therapy is not necessary 1

Timing of First Antibiotic Dose

For patients admitted through the emergency department, administer the first antibiotic dose while still in the ED (moderate recommendation, level III evidence) 1, 2, 3

This timing recommendation reduces mortality risk 2, 3

Key Changes from 2007 to 2019 Guidelines

• Macrolide monotherapy downgraded from strong to conditional recommendation for outpatients, based on local resistance patterns 1
• Healthcare-associated pneumonia category abandoned—emphasis shifted to local epidemiology and validated risk factors for MRSA/Pseudomonas 1
• Procalcitonin not recommended to determine need for initial antibacterial therapy 1
• Corticosteroids not routinely recommended except possibly for refractory septic shock 1
• Routine follow-up chest imaging not recommended unless clinically indicated 1

Critical Pitfalls to Avoid

• Avoid macrolide monotherapy in areas with >25% pneumococcal macrolide resistance to prevent treatment failure 1, 2
• Do not delay antibiotic administration in hospitalized patients—give first dose in ED 2, 3
• Do not automatically escalate to broad-spectrum antibiotics without documented risk factors for resistant organisms 2
• Obtain blood and sputum cultures before initiating antibiotics when treating for MRSA or Pseudomonas to allow targeted de-escalation 1, 2
• Do not extend therapy beyond 7 days in responding patients without specific indications, as this increases resistance risk 2