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, respiratory viruses and atypical pathogens (Legionella spp., Mycoplasma spp., Chlamydia pneumoniae). Staphylococcus aureus comprises <2% of CAP, but should be considered 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 anti-Pseudomonal or anti-MRSA 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 (if Legionella Risk Score >/= 4), Influenza PCR, respiratory viral panel.
For patients started on empiric coverage for MRSA, a nasal MRSA PCR will be obtained on admission; a negative nasal MRSA PCR(NPV=97%) or negative respiratory culture without MRSA have high negative predictive values. De-escalation of anti-MRSA coverage is recommended.
See separate pages for therapeutic management of viral pathogens (http://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

Three (3) days of antibiotics may be considered for adult inpatients with NON-SEVERE CAP who achieve rapid clinical stability. The majority of patients should be treated no more than 5 days, as most will achieve clinical stability within 48-72 hours. (see 2025 ATS guideline)
Patients with pneumonia due to MRSA or Pseudomonas 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)

Severity

All Severity

Patients should be assessed for risk factors (Table 1) and severity (Table 2) to determine empiric therapy choice.

Table 1: Risk Factors to Consider

History of MRSA respiratory culture in past 1 year

History of Pseudomonas respiratory culture in past 1 year

Prior hospitalization AND anti-pseudomonal or anti-MRSA IV antibiotic in past 90 days

Influenza activity

Legionella prevalence or concern for outbreak

Legionella Risk Score(1 point each): no sputum,T>39.4C,CRP > 18.7, LDH > 225, NA < 133 and Platelets <171. Score >/= 4 validates need for a PCR respiratory test.

Underlying immunocompromising conditions

Table 2: Severity Criteria

One Major or 3 Minor Criteria indicate Severe CAP

Major:

Respiratory failue and intubation

Shock/Vasopressors

Minor:

RR>30

PaO2/FiO2 <250

Multilobar infiltrates

Confusion/disorientation

Uremia (BUN >20)

Leukopenia (WBC <4)

Thrombocytopenia (Plt <100)

Hypothermia (T <36C)

Hypotension requiring IVF

Mild-Moderate

NON-SEVERE

Outpatient community-acquired pneumonia (CAP):

RISK GROUP	STANDARD REGIMEN
No comorbidities or risk factors (see Table 1) for MRSA or Pseudomonas	Amoxicillin 1 gm TID OR Doxycycline 100 mg PO BID
With comorbities (chronic heart, lung, liver, or renal, DM, alcoholism, malignancy or asplenia)	Amoxcillin/clavulanate 875/125 mg PO BID OR cefuroxime 500 mg PO BID AND Doxycline 100 mg PO BID OR Azithromycin 500 mg PO daily
With comorbidities AND severe beta-lactam allergy	Levofloxacin 750 mg PO daily.

Inpatient, NON-SEVERE, community-acquired pneumonia (CAP)

Empiric MRSA or Pseudomonas coverage is not necessary in patients with non-severe CAP without risk factors (see table 1).
Patients with non-severe CAP and prior hospitalization or IV antibiotics in the last 90 days should have blood and respiratory cultures collected. Therapy may then be escalated to include MRSA or Pseudomonas if cultures return positive.
*Recommend de-escalation of anti-MRSA ( MRSA nares with 97% NPV) and anti-pseudomonal agents at 48 hours if cultures are negative for these pathogens.

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

RISK GROUP	EMPIRIC THERAPY	DIAGNOSTICS
Standard Regimen WITHOUT Risk Factors for MRSA or Pseudomonas (Table 1)	Ceftriaxone 1 g IV q24h + Azithromycin 500 mg PO/IV q24h Levofloxacin 750 mg PO/IV (SEVERE beta-lactam allergy)	Blood and respiratory cultures NOT needed Legionella urine antigen if risk factors (see Table 1) Basic respiratory virus PCR panel, if high activity
Prior Positive MRSA Culture in last year*	Ceftriaxone 1 g IV q24h + Azithromycin 500 mg PO/IV q24h + Linezolid 600 mg PO/IV q12h OR Vancomycin Levofloxacin 750 mg PO/IV + Linezolid 600 mg PO/IV q12h OR Vancomycin (SEVERE beta-lactam allergy)	Blood cultures Respiratory culture Legionella urine antigen if risk factors Basic respiratory virus PCR panel, if high activity
Prior Positive Pseudomonas Culture in last year*	Piperacillin/tazobactam 3.375 g IV q8h extended infusion + Azithromycin 500 mg PO/IV q24h Cefepime 1 g IV q6h + Azithromycin 500 mg PO/IV q24h (MILD penicillin allergy) Levofloxacin 750 mg PO/IV q24h + Azithromycin 500 mg PO/IV q24h + Linezolid 600 mg PO/IV q12h OR Vancomycin (SEVERE beta-lactam allergy)	Blood cultures Respiratory culture Legionella urine antigen if risk factors
Prior Hospitalization and IV Antibiotics in Last 90 days *	Azithromycin 500 mg PO/IV q24h + Ceftriaxone 1 g IV q24h	Blood cultures Respiratory culture Legionella urine antigen if risk factors

Severe

Inpatient, SEVERE, community-acquired pneumonia (CAP)

*Recommend de-escalation of anti-MRSA (MRSA nares= 97% NPV) and anti-pseudomonal agents at 48 hours if cultures are negative for these pathogens.

RISK GROUP	EMPIRIC THERAPY	DIAGNOSTICS
Standard Regimen WITHOUT Risk Factors for MRSA or Pseudomonas	Ceftriaxone 1 g IV q24h + Azithromycin 500 mg PO/IV q24h Levofloxacin 750 mg PO/IV (SEVERE beta-lactam allergy)	Blood cultures Respiratory culture Legionella urinary antigen and culture S. pneumoniae urinary antigen Basic Respiratory viral panel
Prior Positive MRSA Culture in last year*	Ceftriaxone 1 g IV q24h + Azithromycin 500 mg PO/IV q24h + Linezolid 600 mg PO/IV q12h OR Vancomycin Levofloxacin 750 mg PO/IV + Linezolid 600 mg PO/IV q12h OR Vancomycin to above regimen (SEVERE beta-lactam allergy)	See above
Prior Positive Pseudomonas Culture in last year*	Piperacillin/tazobactam 3.375 g IV q8h extended infusion + Azithromycin 500 mg PO/IV q24h Cefepime 1 g IV q6h + Azithromycin 500 mg PO/IV q24h (MILD penicillin allergy) Levofloxacin 750 mg PO/IV+ Linezolid 600 mg PO/IV q12h OR Vancomycin (SEVERE beta-lactam allergy)	See above
Prior Hospitalization and IV Antibiotics in last 90 days (3 months)*	Azithromycin 500 mg PO/IV q24h + Ceftriaxone 1 gram IV q24h	See above

Severe & Complicated

Pathogen-specific therapy and duration

Note: Agents and durations below are intended for adult immunocompetent patients.

Pathogen	Primary Agent(s)	Alternative Agent(s)	Notes
Bordetella pertussis or parapertussis	Azithromycin 500mg PO/IV q24h x3 days	Bactrim DS 2 tablets BID x14days	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 Pneumonia	Azithromycin 500mg PO/IV q24h x3days	Levofloxacin 750mg PO/IV q24h x7days OR Moxifloxacin 400 mg PO/IV q24 x7days OR Doxycycline 100 mg PO/IV q12 x 7 days.
Mycoplasma Pneumonia	Azithromycin 500 mg PO/IV q24h x3 days	Doxycycline 100 mg PO/IV q12h x7days OR levofloxacin 750mg PO/IV q24h x5-7days	Resistance to azithromycin is increasing globally, but remains low in US. Consider alternative agent if poor response. Recommend Transplant ID evaluation for post-lung transplant cases with M. pneumoniae as combination therapy may be considered.
Streptococcus pneumoniae	Inpatient: Ceftriaxone 1g IV q24h x5 days Outpatient: Amoxicillin 1g PO q8h x5days	Levofloxacin 750 mg PO/IV q24h x5days OR Moxifloxacin 400 mg PO/IV q24h x5days OR Cefuroxime 500 mg PO q12h x5days	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 and follow up susceptibility information for optimal agent selection
Legionella pneumophila	Azithromycin 500 mg PO/IV q24h x5-10 days	Levofloxacin 750 mg PO/IV q24h x5-10days	Duration of therapy depends on clinical response; immunocompromised may require longer duration
Methicillin-Sensitive Staphylococcus aureus (MSSA)	IP: Cefazolin 2g IV q8h x7days OP: Cefadroxil 500 mg PO q12h x7 days	Cephalexin 500 mg PO q6h x7days OR Linezolid 600 mg PO/IV q12h x7days OR TMP/SMX weight-based dosing q12h x7days	Bacteremia: Consult ID Evaluate for complications, including parapneumonic effusion, empyema, necrotizing pneumonia, or abscess which may require extended duration of therapy Use susceptibility data to guide agent selection for oral transition Clindamycin should be avoided due to risk of resistance and adverse drug events.
Methicillin-Resistant Staphylococcus aureus (MRSA)	Linezolid 600 mg PO/IV q12h x7days	Vancomycin IV, dosed per pharmacy, 7d TMP-SMX weight-based dosing q12h x7 days

Diagnosis-Specific Information

De-escalation Guidance when diagnostics are negative for a specific pathogen

INITIAL INPATIENT THERAPY

ORAL SWITCH (STANDARD DURATION)

Ceftriaxone 1g q24h + azithromycin 500 mg PO/IV q24h OR

Ceftriaxone 1g q24h + Doxycycline 100 mg PO/IV q12h * see attachment showing beta lactam

+ doxycycline has lower 30-day and 90-day mortality rates.

Cefuroxime 500 mg PO BID (3- 5 days total) + azithromycin 500 mg PO daily (3 days total)

Augmentin 875 mg PO BID ( 5 days total) + Azithromycin 500 mg PO ( 3 days total)

Vancomycin + piperacillin/tazobactam 3.375g IV q8h EI + azithromycin 500 mg PO/IV q24h

Amoxicillin/clavulanate 875/125 mg PO BID (3- 5 days total) + azithromycin 500 mg 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 oral fluoroquinolone for discharge. For example, avoid a switch from an intravenous beta-lactam to oral fluoroquinolone for discharge.

References

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

Jones, Barbara E, et al. “Diagnosis and Management of Community-Acquired Pneumonia. An Official American Thoracic Society Clinical Practice Guideline.” PubMed, 18 July 2025, https://doi.org/10.1164/rccm.202507-1692st.