Pneumonia, Community-Acquired (CAP)

Criteria & Principles

Community-acquired Pneumonia (CAP) symptom onset occurs prior to or within the first 2 days of hospital admission.
Pathogens to consider include:
- Streptococcus pneumoniae
- Haemophilus influenzae
- Moraxella catarhallis
- Atypical pathogens (Legionella spp., Mycoplasma spp., Chlamydophila spp.)
- Staphylococcus aureus comprises <2% of CAP, but is more prevalent during influenza season
Respiratory and blood cultures are recommended for the following patients: severe CAP, those with a personal history of MRSA or Pseudomonas aeruginosa, or patients previously hospitalized and treated with IV antibiotics within the last 90 days.
Additional diagnostic tests are appropriate for patients with severe CAP and/or risk factors: S. pneumoniae urine antigen, Legionella urine antigen, Legionella respiratory culture, Influenza PCR, respiratory viral panel, MRSA nasal PCR (if empirically covering MRSA)
For patients started on empiric coverage for MRSA, a negative nasal MRSA PCR or negative respiratory culture without MRSA at 48 hours have high negative predictive values. De-escalation of anti-MRSA coverage is recommended. Holding MRSA coverage while waiting for a nasal MRSA PCR test is recommended for non-severe patients previously hospitalized and treated with IV antibiotics within the last 90 days.
Aspiration pneumonia does not require additional anaerobic coverage unless abscess or empyema is suspected.
Healthcare-Associated Pneumonia (HCAP) terminology has been abandoned - see below treatment recommendations
See separate pages for therapeutic management of viral pathogens (COVID-19, Influenza, RSV), which are all included in the Basic Respiratory Virus PCR Panel test.
The Extended Respiratory Pathogen PCR Panel test is restricted to the following:
- Inpatient (and ED) ≤3 days from admission
- Immunocompromised / Transplant
- Significant underlying lung disease

Treatment

Duration

3-7 days based on clinical improvement

Three (3) days of antibiotics may be considered for immunocompetent adult inpatients with NON-SEVERE CAP who achieve rapid clinical stability. The majority of patients should be treated for no more than 5 days, as most will achieve clinical stability within 48-72 hours.
Patients with pneumonia due to MRSA or Pseudomonas aeruginosa should be treated for 7 days (See HAP/VAP guideline).
High-dose (i.e. 500 mg) azithromycin achieves high concentrations in lung tissue that persist for several days. For most hospitalized patients, azithromycin can be stopped after three daily doses of 500 mg.
Some pathogens require specific durations based on agent selection (See Pathogen-specific recommendations below)

Severity

All Severity

Decisions regarding empiric therapy should be based on disease severity (Table 1) and risk factors (Table 2) for negative outcomes and specific pathogens, including MRSA and Pseudomonas aeruginosa.

Table 1: Severity Criteria

One Major or Three Minor Criteria indicate Severe CAP

Major

Respiratory failure and intubation

Shock / Vasopressors

Minor

RR > 30

PaO2/FiO2 < 250

Multilobar infiltrates

Confusion / disorientation

Uremia (BUN > 20)

Leukopenia (WBC < 4) *due to infection alone (i.e., not chemotherapy induced)

Thrombocytopenia (platelets < 100)

Hypothermia (temperature < 36C)

Hypotension requiring IV fluids

Table 2: Risk Factors to Consider

History of MRSA in respiratory culture in past 1 year

History of Pseudomonas aeruginosa in respiratory culture in past 1 year

Prior hospitalization AND IV antibiotic use in past 90 days

Influenza and COVID-19 activity

Legionella prevalence or concern for outbreak

Underlying immunocompromising conditions

Mild-Moderate

NON-SEVERE

OUTPATIENT Community-Acquired Pneumonia
Risk Group	Standard Regimen
No comorbidities or risk factors (see Table 2) for MRSA or Pseudomonas	Amoxicillin 1g PO TID OR Doxycycline 100mg PO BID NOTE: macrolide monotherapy is not recommended due to >25% pneumococcal resistance rates
With comorbidities (chronic heart, lung, liver, or renal disease; DM; alcoholism; malignancy; asplenia)	Amoxicillin/clavulanate 875/125mg PO BID OR Cefuroxime 500mg PO BID AND Doxycycline 100mg PO BID OR Azithromycin 500mg PO daily
With comorbidities AND severe beta-lactam allergy	Levofloxacin 750mg PO daily

INPATIENT NON-SEVERE Community-Acquired Pneumonia *Empiric MRSA or Pseudomonas aeruginosa* coverage is not necessary in patients with NON-SEVERE CAP without risk factors (see Table 2)** Patients with NON-SEVERE CAP + Prior Hospitalization + IV antibiotic administration in the past 90 days should have blood and respiratory cultures collected. Therapy may then be escalated to include MRSA or Pseudomonas aeruginosa if isolated on culture.
Risk Group	Empiric Therapy^	Diagnostics
Standard Regimen WITHOUT Risk Factors for MRSA or Pseudomonas	Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO q24h SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO daily	Blood and respiratory cultures NOT needed Legionella urine antigen if risk factors (see Table 2) Basic respiratory virus PCR panel, if high activity
Prior Positive MRSA Culture in the last year*	Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin	Blood cultures Respiratory culture Legionella urine antigen if risk factors (Table 2) MRSA nasal PCR if empirically covering with anti-MRSA agent (e.g., vancomycin) Basic respiratory virus PCR panel, if high activity
Prior Positive Pseudomonas Culture in the last year*	Piperacillin/tazobactam 3.375g IV q8h extended infusion + Azithromycin 500mg IV/PO q24h MILD penicillin allergy: Cefepime 1g IV q6h + Azithromycin 500mg IV/PO q24h SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h
Prior Hospitalization and IV Antibiotics in the last 90 days*	Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO q24h SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO daily
Prior Hospitalization and IV Antibiotics in the last 90 days AND positive MRSA nares PCR*	Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin

Severe

SEVERE

INPATIENT SEVERE Community-Acquired Pneumonia
Risk Group	Empiric Therapy^	Diagnostics
Standard Regimen WITHOUT Risk Factors for MRSA or Pseudomonas	Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO q24h SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h	Blood cultures Respiratory culture MRSA nasal PCR if empirically covering with anti-MRSA agent (e.g., vancomycin) Legionella urinary antigen and culture S. pneumoniae urinary antigen Respiratory viral panel
Prior Positive MRSA Culture in the last year*	Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO + Linezolid 600mg IV/PO q12h OR Vancomycin SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin
Prior Positive Pseudomonas Culture in the last year*	Piperacillin/tazobactam 3.375g IV q8h extended infusion + Azithromycin 500mg IV/PO q24h MILD penicillin allergy: Cefepime 1g IV q6h + Azithromycin 500mg IV/PO q24h SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h
Prior Hospitalization and IV Antibiotics in the last 90 days*	Piperacillin/tazobactam 3.375g IV q8h extended infusion + Azithromycin 500mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin MILD penicillin allergy: Cefepime 1g IV q6h + Azithromycin 500mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin SEVERE beta-lactam allergy: Levofloxacin 750mg IV/PO q24h + Linezolid 600mg IV/PO q12h OR Vancomycin

*Recommend de-escalation of anti-MRSA and anti-pseudomonal agents at 48h if cultures are negative for these pathogens. Empiric anti-MRSA therapy can be discontinued based on a negative MRSA PCR in the appropriate clinical context (See MRSA nares PCR page).

^Recommend PO formulations if patient can tolerate enteral feeding and oral medication, and if gastrointestinal absorption is intact

+Linezolid-induced serotonin syndrome is rare. Use is generally safe in patients on only one serotonergic agent; however, risk may be increased with select agents, multiple concurrent serotonergic agents, and/or higher doses. See the linezolid-induced serotonin syndrome page for further information.

Diagnosis-Specific Information

Pathogen-specific therapy and duration Note: Agents and durations below are intended for adult immunocompetent patients. Consult ID service for patient-specific recommendations.
Pathogen	Primary Agent(s)	Alternative Agent(s)	Notes
Bordetella pertussis or parapertussis	Azithromycin 500 mg IV/PO q24h x 3 days	Bactrim DS 2 tablets BID x 14 days	Treatment is indicated for all patients with cough < 3 weeks duration and for at-risk patients with cough >3 and < 6 weeks duration Post-exposure prophylaxis is indicated for household and other high-risk contacts
Chlamydia pneumoniae	Azithromycin 500 mg IV/PO q24h x 3 days	Levofloxacin 750 mg IV/PO q24h x 7 days OR Doxycycline 100 mg IV/PO q12h x 7 days
Mycoplasma pneumoniae	Azithromycin 500 mg IV/PO q24h x 3 days	Doxycycline 100 mg IV/PO q12h x 7 days OR Levofloxacin 750 mg IV/PO q24h x 5-7 days	Resistance to azithromycin is increasing globally but remains low in the U.S. Consider altnerative agent if poor response. Recommend Transplant ID evaluation for post-lung transplant cases with M. pneumoniae since combination therapy may be considered.
Streptococcus pneumoniae	Inpatient: Ceftriaxone 1g IV q24h x 3-5 days Outpatient: Amoxicillin 1g PO q8h x 3-5 days	Levofloxacin 750 mg IV/PO q24h x 3-5 days OR Cefuroxime 500 mg PO q12h x 3-5 days	Transition from IV ceftriaxone to oral therapy when there is clinical improvement. Evaluate for complications and additional sites of infection as indicated by clinical presentation and response. For pneumonia plus secondary bacteremia, suggest 7 day duration. Follow-up susceptibility information for optimal agent selection.
Legionella pneumophila	Azithromycin 500 mg IV/PO q24h x 5-10 days	Levofloxacin 750 mg IV/PO q24h x 5-10 days	Duration of therapy depends on clinical response. Immunocompromised patients may require longer durations.
Methicillin-sensitive Staphylococcus aureus (MSSA)	Inpatient: Cefazolin 2g IV q8h x 7 days Outpatient: Cefadroxil 500 mg PO q12h x 7 days	Cephalexin 500 mg PO q6h x 7 days OR Linezolid 600 mg IV/PO q12h x 7 days OR Bactrim weight-based dosing q12h x 7 days	Bacteremia: Consult ID Evaluate for complications including parapneumonic effusion, empyema, necrotizing pneumonia, or abscess which may require extended durations of therapy. Use susceptibility data to guide agent selection for oral transition. Clindamycin should be avoided due to risk for resistance and adverse drug events.
Methicillin-resistant Staphylococcus aureus (MRSA)	Linezolid 600 mg IV/PO q12h x 7 days	Vancomycin IV, dosed per pharmacy, x 7 days OR Bactrim weight-based dosing q12h x 7 days

De-escalation Guidance when Diagnostics are Negative for a Specific Pathogen
Initial Inpatient Therapy	Oral Switch (standard duration)
Ceftriaxone 1g IV q24h + Azithromycin 500mg IV/PO q24h	Cefuroxime 500mg PO BID (3-5 days total) + Azithromycin 500mg PO daily (3 days total)
Vancomycin + Piperacillin/tazobactam 3.375g IV q8h (EI 4h) + Azithromycin 500mg IV/PO q24h	Amoxicillin/clavulanate 875/125mg PO BID (3-5 days total) + Azithromycin 500mg PO daily (3 days total)

Renal dosing adjustments are required for ampicillin/sulbactam, amoxicillin/clavulanate, piperacillin/tazobactam, cefuroxime, and vancomycin.
We recommend AGAINST beta-lactam class switching. For example, avoid a switch from cephalosporin to a penicillin class oral agent for discharge.
We recommend AGAINST a class switch to an oral fluoroquinolone for discharge. For example, avoid a switch from an IV beta-lactam to an oral fluoroquinolone at discharge.

References

Jones et al. Am J Respir Crit Care Med. 2025. doi: 10.1164/rccm.202507-1692ST

Metlay et al. Am J Respir Crit Care Med Vol 200, Iss 7, pp e45–e67, Oct 1, 2019