Orion Cardiology, PLLC : Community Acquired Pneumonia NEJM 2023

Sunday, May 11, 2025

Key Clinical Take-Home Points

Diagnosis requires compatible symptoms plus a new infiltrate on chest imaging.
Outpatients with mild disease can be treated empirically; however, test for SARS-CoV-2 and influenza.
Hospitalized patients benefit from a broad, front-loaded microbiology work-up to guide pathogen-directed therapy.
Initial antibiotic choice hinges on disease severity, comorbidities, and local resistance patterns.
CAP is now viewed as a multi-system illness with important long-term sequelae (cardiac, pulmonary, neurologic).

Metric	Data
US hospitalizations/yr	≈1.5 million (650/100,000 adults)
High-risk groups	Age >65, COPD/asthma, CHF/CAD, diabetes, malnutrition, immunocompromise, smoking, excess alcohol

Group	Typical Pathogens	Notes
Core bacteria	Streptococcus pneumoniae MSSA H. influenzae Atypicals: Mycoplasma, Chlamydophila, Legionella	Cause majority of ambulatory & ward cases
Respiratory viruses	SARS-CoV-2, Influenza A/B, RSV, Parainfluenza, hMPV, Rhinovirus	Rapid PCR panels recommended on admission
Uncommon / MDR	MRSA, Pseudomonas, ESBL-Enterobacteriaceae, fungi (e.g., Pneumocystis), MERS-CoV	Consider with structural lung disease, prior IV antibiotics, immunosuppression

CURB-65 ≤1 ➔ treat as outpatient.
CURB-65 = 2 ➔ short stay/observation.
CURB-65 ≥3 or any ATS/IDSA major criterion (invasive ventilation or vasopressor-requiring shock) ➔ ICU level care.

Setting	Preferred Regimens
Healthy outpatient, no antibiotics <3 mo	Amoxicillin 1 g TID or Doxycycline 100 mg BID
Comorbidities / recent antibiotics	Amox-clav 875 mg BID + macrolide (azithro) or doxycycline Alt: Levofloxacin 750 mg daily
Ward (no MRSA/PSA risk)	Ceftriaxone 1–2 g daily + Azithro 500 mg daily or Levofloxacin 750 mg daily monotherapy
ICU / severe CAP	If MRSA risk ➔ add Vancomycin 15–20 mg/kg q8–12 h or Linezolid 600 mg BID If PSA risk ➔ use anti-pseudomonal β-lactam (Pip-Tazo 4.5 g q6 h or Cefepime 2 g q8 h) + Azithro

Obtain sputum Gram stain/culture, blood cultures, urine Ag tests (Strep. pneumoniae, Legionella) and multiplex viral PCR on admission.
De-escalate or stop antibiotics when:
- Viral pathogen identified and no evidence of bacterial coinfection (low WBC, CRP <150 mg/L, procalcitonin <0.25 ng/mL).
- MRSA nasal PCR negative ➔ stop anti-MRSA agent.
Typical duration: 5 days (≥48 h afebrile & clinically stable). Certain pathogens/complications require longer courses.

Early glucocorticoids (e.g., Hydrocortisone 200 mg/day IV taper) improve survival in severe, non-viral CAP; avoid in influenza or aspergillosis.
Vaccinate for influenza, Covid-19, and pneumococcus; counsel on smoking cessation & alcohol moderation.
Arrange primary-care follow-up within 1 week; routine follow-up CXR only if high risk for malignancy or persistent symptoms.

30-day mortality: ~10–15% of hospitalized cases; 1-yr mortality rises to 30–35%, especially with ICU admission.
Increased risk of MI, stroke, arrhythmia, chronic lung dysfunction, cognitive decline, and rehospitalization.

Source: File TM Jr, Ramirez JA. “Community-Acquired Pneumonia.” NEJM 2023;389:632-41.

Risk factors for MRSA/MSSA and Pseudomonas Aeruginosa in CAP

Pathogen	Established Community-Acquired Risk Factors^*
Staphylococcus aureus (incl. CA-MRSA)	Recent (< 2 weeks) influenza or other viral respiratory infection Cavitary or necrotizing pneumonia on imaging Severe CAP requiring ICU admission or septic shock History of colonization or infection with MRSA Chronic skin/soft-tissue infection, abscesses, or active I.V. drug use Hemodialysis or chronic kidney disease (esp. end-stage) Diabetes mellitus or structural lung disease (COPD, bronchiectasis, cystic fibrosis) Immunosuppression or prolonged corticosteroid therapy Residence in crowded settings (long-term care, prisons, athletic facilities, military)
Pseudomonas aeruginosa	Structural lung disease (bronchiectasis, severe COPD FEV₁ < 50%, cystic fibrosis) Prior colonization or documented infection with P. aeruginosa Frequent or recent (< 90 days) broad-spectrum antibiotics or systemic corticosteroids Recent hospitalization ≥ 48 h, mechanical ventilation, or tracheostomy Immunosuppression (HIV, neutropenia, solid-organ or stem-cell transplant) Malnutrition or low body-mass index Recurrent COPD exacerbations requiring oral steroids/antibiotics Chronic home oxygen therapy or nebulizer use

Pathogen

Established Community-Acquired Risk Factors^*

Staphylococcus aureus
(incl. CA-MRSA)

Recent (< 2 weeks) influenza or other viral respiratory infection
Cavitary or necrotizing pneumonia on imaging
Severe CAP requiring ICU admission or septic shock
History of colonization or infection with MRSA
Chronic skin/soft-tissue infection, abscesses, or active I.V. drug use
Hemodialysis or chronic kidney disease (esp. end-stage)
Diabetes mellitus or structural lung disease (COPD, bronchiectasis, cystic fibrosis)
Immunosuppression or prolonged corticosteroid therapy
Residence in crowded settings (long-term care, prisons, athletic facilities, military)

Pseudomonas aeruginosa

Structural lung disease (bronchiectasis, severe COPD FEV₁ < 50%, cystic fibrosis)
Prior colonization or documented infection with P. aeruginosa
Frequent or recent (< 90 days) broad-spectrum antibiotics or systemic corticosteroids
Recent hospitalization ≥ 48 h, mechanical ventilation, or tracheostomy
Immunosuppression (HIV, neutropenia, solid-organ or stem-cell transplant)
Malnutrition or low body-mass index
Recurrent COPD exacerbations requiring oral steroids/antibiotics
Chronic home oxygen therapy or nebulizer use

^*Adapted from IDSA/ATS Community-Acquired Pneumonia Guidelines (2019) and contemporary literature reviews on multidrug-resistant organisms in CAP.