2019 ATS/IDSA Guidelines for Community-Acquired Pneumonia
Severity Assessment and Site-of-Care Decision
Use a validated severity score (PSI or CURB-65) combined with clinical judgment to determine hospitalization need. 1
- PSI Classes I–III: Treat outpatient unless unstable comorbidities exist 1
- PSI Classes IV–V: Consider hospitalization; Class V strongly indicates inpatient care 1, 2
- CURB-65 ≥2: Hospitalization recommended 1
- ICU admission criteria: Meet one major criterion (septic shock requiring vasopressors OR mechanical ventilation) OR ≥3 minor criteria (confusion, RR ≥30/min, SBP <90 mmHg, multilobar infiltrates, PaO₂/FiO₂ <250, uremia, leukopenia, thrombocytopenia, hypothermia, hypotension requiring aggressive fluids) 1
Outpatient Antibiotic Regimens
Previously Healthy Adults (No Comorbidities)
- First-line: Amoxicillin 1 g PO three times daily for 5–7 days 3
- Alternative: Doxycycline 100 mg PO twice daily 3
- Macrolides (azithromycin 500 mg day 1, then 250 mg daily; clarithromycin 500 mg twice daily): Use ONLY when local pneumococcal macrolide resistance is <25% 3
Adults with Comorbidities or Recent Antibiotic Use
- Combination therapy: β-lactam (amoxicillin-clavulanate 875/125 mg twice daily, cefpodoxime, or cefuroxime) PLUS macrolide (azithromycin or clarithromycin) OR doxycycline 100 mg twice daily 3
- Alternative monotherapy: Respiratory fluoroquinolone (levofloxacin 750 mg daily OR moxifloxacin 400 mg daily) 3
Inpatient Antibiotic Regimens (Non-ICU)
Two equally effective regimens with strong evidence: 3
- β-lactam + macrolide: Ceftriaxone 1–2 g IV daily PLUS azithromycin 500 mg IV/PO daily 3
- Alternative β-lactams: cefotaxime 1–2 g IV every 8 hours OR ampicillin-sulbactam 3 g IV every 6 hours 3
- Respiratory fluoroquinolone monotherapy: Levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 3
ICU Antibiotic Regimens (Severe CAP)
Combination therapy is mandatory for all ICU patients—monotherapy increases mortality. 3
- Preferred regimen: 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) 3
- Alternative β-lactams: cefotaxime 1–2 g IV every 8 hours OR ampicillin-sulbactam 3 g IV every 6 hours 3
Special Pathogen Coverage (Risk Factor–Based)
Pseudomonas aeruginosa Coverage
Add antipseudomonal therapy ONLY when risk factors present: 3
- Structural lung disease (bronchiectasis, cystic fibrosis)
- Recent hospitalization with IV antibiotics (≤90 days)
- Prior respiratory isolation of P. aeruginosa
- Chronic broad-spectrum antibiotic exposure (≥7 days in past month)
Regimen: 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 hours OR levofloxacin 750 mg IV daily PLUS aminoglycoside (gentamicin or tobramycin 5–7 mg/kg IV daily) 3
MRSA Coverage
Add MRSA therapy ONLY when risk factors present: 3
- Prior MRSA infection/colonization
- Recent hospitalization with IV antibiotics (≤90 days)
- Post-influenza pneumonia
- Cavitary infiltrates on imaging
Regimen: Vancomycin 15 mg/kg IV every 8–12 hours (target trough 15–20 µg/mL) OR linezolid 600 mg IV every 12 hours, added to base regimen 3
Duration of Therapy
- Minimum: 5 days AND afebrile for 48–72 hours with ≤1 sign of clinical instability 3
- Uncomplicated CAP: 5–7 days total 3
- Extended duration (14–21 days): Required for Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli 3
Transition from IV to Oral Therapy
Switch when ALL criteria met: 3
- Hemodynamically stable (SBP ≥90 mmHg, HR ≤100 bpm)
- Clinically improving
- Afebrile for 48–72 hours
- RR ≤24 breaths/min
- Oxygen saturation ≥90% on room air
- Able to take oral medications
- Normal GI function
Typical timing: Hospital day 2–3 3
Diagnostic Testing
- Blood cultures and sputum Gram stain/culture: Obtain before antibiotics in all hospitalized patients 3
- Urinary antigen testing: Consider for Legionella pneumophila serogroup 1 in severe CAP or ICU patients 3
Critical Timing Considerations
Administer the first antibiotic dose in the emergency department immediately upon diagnosis. Delays >8 hours increase 30-day mortality by 20–30%. 3
Key Changes from 2007 to 2019 Guidelines
- Macrolide monotherapy downgraded from strong to conditional recommendation for outpatients; use only when local resistance <25% 3
- Healthcare-associated pneumonia (HCAP) category abandoned—shift to validated risk factors for MRSA/Pseudomonas rather than blanket broad-spectrum coverage 3
- Shorter antibiotic durations emphasized: 5–7 days for uncomplicated CAP replaces older 7–10 day recommendations 3
Common Pitfalls to Avoid
- Never use macrolide monotherapy in hospitalized patients—inadequate coverage for typical pathogens like S. pneumoniae 3
- Never use macrolide monotherapy when local resistance ≥25%—leads to treatment failure and breakthrough bacteremia 3
- Never add broad-spectrum agents (antipseudomonal or MRSA coverage) without documented risk factors—promotes resistance without benefit 3
- Never delay antibiotic administration >8 hours—significantly increases mortality 3
- Never use fluoroquinolone monotherapy in ICU patients—combination therapy is mandatory 3
Flowchart: CAP Management Algorithm
┌─────────────────────────────────────┐
│ Adult with suspected CAP │
│ (obtain CXR, pulse oximetry) │
└──────────────┬──────────────────────┘
│
▼
┌──────────────────────────────────────┐
│ Severity Assessment: │
│ • PSI score or CURB-65 │
│ • Hypoxemia (SpO₂ <92%) │
│ • Comorbidities │
└──────────────┬───────────────────────┘
│
┌──────┴──────┐
│ │
▼ ▼
┌─────────────┐ ┌──────────────────┐
│ OUTPATIENT │ │ HOSPITALIZE │
│ PSI I-III │ │ PSI IV-V or │
│ CURB-65 0-1 │ │ CURB-65 ≥2 │
└──────┬──────┘ └────────┬─────────┘
│ │
▼ ▼
┌─────────────────┐ ┌──────────────────────┐
│ No comorbidities│ │ ICU criteria met? │
│ • Amoxicillin │ │ (1 major OR ≥3 minor)│
│ 1g TID │ └──────┬───────────────┘
│ OR │ │
│ • Doxycycline │ ┌────┴────┐
│ 100mg BID │ │ │
└─────────────────┘ ▼ ▼
┌─────────┐ ┌──────────┐
┌─────────────────┤ Non-ICU │ │ ICU │
│ Comorbidities └─────────┘ └──────────┘
│ • β-lactam + │ │
│ macrolide ▼ ▼
│ OR ┌──────────┐ ┌──────────────┐
│ • Fluoroquinolone│Ceftriaxone│Ceftriaxone 2g│
│ │1-2g IV + │IV daily + │
└──────────────────│Azithro │Azithro 500mg │
│500mg │IV daily │
│daily │OR │
│OR │Fluoroquinolone│
│Fluoroquino│ │
│lone alone │ │
└─────┬─────┴──────┬───────┘
│ │
▼ ▼
┌──────────────────────────┐
│ Risk factors present? │
│ • Pseudomonas │
│ • MRSA │
└──────┬───────────────────┘
│
┌─────┴─────┐
│ │
▼ ▼
┌─────────┐ ┌─────────┐
│ NO │ │ YES │
│Continue │ │Add │
│base │ │targeted │
│regimen │ │coverage │
└────┬────┘ └────┬────┘
│ │
└─────┬──────┘
▼
┌──────────────────┐
│ Clinical stability│
│ • Afebrile 48-72h│
│ • Stable vitals │
│ • SpO₂ ≥90% │
└────────┬─────────┘
▼
┌──────────────────┐
│ Switch to PO │
│ Continue 5-7 days│
│ total │
└──────────────────┘