Community Acquired Pneumonia

Welcome back to AudioBoards, today we break down CAP management from diagnosis to disposition and antibiotic selection. Learn how to distinguish pneumonia from other respiratory illnesses, apply CURB-65 and PSI scoring, identify patients who need hospitalization or ICU care, select guideline-based empiric antibiotics, recognize when MRSA or Pseudomonas coverage is warranted, and determine the optimal duration of therapy.

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Welcome back to AudioBoards. Today we're covering one of the most important conditions in internal medicine: community-acquired pneumonia, or CAP.

CAP remains one of the leading infectious causes of hospitalization and death worldwide. Yet despite seeing it every day, clinicians frequently struggle with three questions:

Is this really pneumonia?

Does this patient need admission?

What's the right antibiotic regimen?

By the end of this episode, you'll have a practical framework for evaluating, risk stratifying, and treating CAP from the clinic to the ICU. We'll focus on the latest evidence and guideline-based management.

Let's start with the basics. What qualifies as community-acquired pneumonia?

CAP is an acute infection of the lung parenchyma acquired outside the hospital.

To diagnose CAP, you need two things:

First, a clinically compatible syndrome:

Cough

Fever or chills

Dyspnea

Pleuritic chest pain

Sputum production

Fatigue

And second, evidence of a new infiltrate on chest imaging.

Symptoms alone are not enough. A patient with cough and fever but no infiltrate may have bronchitis, influenza, or another respiratory infection rather than pneumonia.

Who Gets CAP?

Risk factors include:

Age over 65

Smoking

COPD

Asthma

Heart failure

Diabetes

Chronic kidney disease

Chronic liver disease

Alcohol use disorder

Immunocompromised states

The incidence and mortality increase substantially with age and comorbid illness.

What organisms should we think about?

The classic board answer remains the most important one:

Typical Bacteria

Streptococcus pneumoniae — most common bacterial cause

Haemophilus influenzae

Moraxella catarrhalis

Atypical Bacteria

Mycoplasma pneumoniae

Chlamydia pneumoniae

Legionella species

Viruses

Influenza

SARS-CoV-2

RSV and other respiratory viruses

Less commonly, but critically important:

Drug-Resistant Organisms

MRSA

Pseudomonas aeruginosa

These should not be covered routinely. Coverage is reserved for patients with validated risk factors.

Patients often present with:

Fever

Productive cough

Dyspnea

Tachypnea

Hypoxemia

On exam you may find:

Crackles

Bronchial breath sounds

Increased tactile fremitus

Egophony

Older adults may be different.

Instead of fever and cough, they may present with:

Confusion

Weakness

Falls

Functional decline

Always keep pneumonia on the differential in elderly patients with unexplained delirium.

When CAP is suspected, obtain:

Basic Workup

Vital signs

Pulse oximetry

CBC

BMP or CMP

Chest imaging

Chest radiography remains the standard initial imaging test.

Lung ultrasound can be very useful when expertise is available.

CT scanning is generally reserved for uncertain diagnoses or complicated cases.

The Most Important Decision: Admit or Not? This is where many clinicians struggle.

Exactly.

Severity assessment determines disposition.

The preferred tool is the Pneumonia Severity Index, or PSI.

CURB-65 remains useful because it's quick and easy.

CURB-65

One point each for:

Confusion

BUN >19 mg/dL

Respiratory rate ≥30

Blood pressure <90 systolic or ≤60 diastolic

Age ≥65

Interpretation

0–1 points:

Usually outpatient treatment

2 points:

Consider hospitalization

3 or more:

Hospital admission likely required

But never let the score replace clinical judgment.

A patient with a low CURB-65 who requires oxygen may still need admission.

And Who Needs ICU-Level Care?

The ATS/IDSA severe CAP criteria are extremely high yield.

Major Criteria

Either one qualifies:

Septic shock requiring vasopressors

Respiratory failure requiring mechanical ventilation

Minor Criteria

Examples include:

Respiratory rate ≥30

PaO2/FiO2 ≤250

Multilobar infiltrates

Confusion

BUN ≥20

Leukopenia

Thrombocytopenia

Hypothermia

Hypotension requiring aggressive fluids

Three or more minor criteria suggest severe CAP and possible ICU admission.

Do all admitted patients need cultures?

No. Routine extensive testing is often low yield.

Consider blood cultures when:

Severe CAP

ICU admission

Concern for MRSA

Concern for Pseudomonas

Recent hospitalization

Immunocompromised patient

Sputum cultures are most useful in severe disease and when resistant pathogens are suspected.

Legionella and pneumococcal urinary antigens may be useful in selected hospitalized patients.

What is the management?

Let's start with the easiest group.

Healthy adults without significant comorbidities that is Outpatient CAP treatment in patients Without Comorbidities

High-dose amoxicillin is preferred.

Doxycycline is a strong alternative.

Macrolide monotherapy should only be used if local pneumococcal resistance is low. Many regions no longer meet this threshold.

What counts as a comorbidity?

Examples include:

COPD

Asthma

Diabetes

CKD

CHF

Chronic liver disease

Malignancy

For these patients:

Beta-lactam plus atypical coverage:

Amoxicillin-clavulanate plus azithromycin

Amoxicillin-clavulanate plus doxycycline

Alternative beta-lactams include cefpodoxime or cefuroxime.

Respiratory fluoroquinolone monotherapy

Examples:

Levofloxacin

Moxifloxacin

However, because of adverse effects and antimicrobial stewardship concerns, many clinicians reserve fluoroquinolones for selected situations.

For hospitalized patients on the general medical floor:

Preferred Regimen

Ceftriaxone plus azithromycin

or

Ampicillin-sulbactam plus azithromycin

Alternative

Respiratory fluoroquinolone monotherapy

The goal is coverage of both typical and atypical organisms.

For ICU patients:

Standard Therapy

Beta-lactam plus macrolide

Examples:

Ceftriaxone plus azithromycin

Cefotaxime plus azithromycin

Alternative:

Beta-lactam plus respiratory fluoroquinolone.

Several studies suggest that macrolide-containing regimens may provide outcome benefits in severe CAP.

When Should We Cover MRSA? Everyone worries about MRSA.

And that's why over-treatment happens.

MRSA coverage is indicated only when risk factors exist.

Examples:

Prior MRSA infection

Prior MRSA respiratory isolation

Recent hospitalization with IV antibiotics

Severe necrotizing pneumonia

Post-influenza bacterial pneumonia

Add:

Vancomycin

or

Linezolid

Do not routinely add MRSA coverage to every pneumonia patient.

When Should We Cover Pseudomonas?

Again, only when risk factors exist.

Examples:

Prior Pseudomonas isolation

Structural lung disease such as bronchiectasis

Recent hospitalization with IV antibiotics

Options include:

Piperacillin-tazobactam

Cefepime

Meropenem

depending on patient factors and local resistance patterns.

What About Corticosteroids? This has been controversial.

Very. Current evidence suggests steroids are not routinely indicated for uncomplicated CAP.

Potential benefit exists in selected patients with severe CAP, especially those with septic shock.

For most ward patients with pneumonia, routine steroid use is not recommended.

Never focus only on antibiotics. Supportive management includes:

Oxygen therapy

IV fluids when appropriate

Bronchodilators if obstructive disease is present

Early mobilization

DVT prophylaxis when hospitalized

Management of sepsis if present

Remember: mortality is often related to respiratory failure and sepsis rather than the infection alone.

Most patients should show improvement within 48 to 72 hours.

Monitor:

Fever curve

Oxygen requirements

Respiratory rate

Heart rate

WBC count

Subjective symptom improvement

If a patient is worsening, reconsider:

Incorrect diagnosis

Resistant pathogen

Empyema

Lung abscess

Pulmonary embolism

Malignancy

Heart failure masquerading as pneumonia

How long should we treat?

This is one of the biggest changes over the years. Long antibiotic courses are usually unnecessary. For most patients:

Minimum 5 days: And continue until:

Afebrile for at least 48 hours

Hemodynamically stable

Clinically improving

Longer courses are reserved for:

MRSA

Pseudomonas

Lung abscess

Empyema

Severe complications

Shorter, targeted therapy improves stewardship and reduces adverse effects.

Let's finish with rapid-fire pearls.

CAP diagnosis requires symptoms plus a new infiltrate.

Streptococcus pneumoniae remains the most important bacterial pathogen.

Use PSI or CURB-65 to help determine disposition.

Ceftriaxone plus azithromycin is the classic inpatient regimen.

Do not routinely cover MRSA or Pseudomonas.

Severe CAP is defined by major or multiple minor ATS/IDSA criteria.

Most patients need only about 5 days of therapy.

Clinical stability—not radiographic resolution—determines when treatment can stop.

Always reassess if the patient fails to improve within 48–72 hours.

So the key takeaway is that CAP management is really about three decisions: confirming the diagnosis, determining the appropriate site of care, and choosing the right antibiotic regimen without over-treating.

Exactly. If you can answer those three questions consistently, you'll manage the vast majority of CAP cases effectively and according to modern evidence-based guidelines.

Thanks for listening to AudioBoards. Stay tuned for more educational content in our next episode! The views and opinions expressed on the AudioBoards Podcast do not necessarily reflect those of our employers. This podcast is for educational purposes only and should not be used to diagnose or treat any medical conditions. It is not a substitute for professional medical advice. Always consult a qualified, board-certified healthcare provider for any medical concern.