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Community & Hospital-Acquired Pneumonia

Name: Community & Hospital-Acquired Pneumonia
Creator: Veli Bakalov, MD

Score it, cover the right bugs, and drain the empyema

Pulmonology·Pulmonary Infections·5 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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CAP needs a new chest x-ray infiltrate for diagnosis; Streptococcus pneumoniae is the most common bacterial cause (rust-colored sputum).
CURB-65 (confusion, BUN over 19, RR ≥30, BP under 90/60, age ≥65): 0–1 outpatient, 2 consider admission, ≥3 admit and consider ICU.
ICU for either major criterion (vasopressor-requiring shock or mechanical ventilation) or ≥3 minor criteria (RR ≥30, PaO2/FiO2 ≤250, multilobar infiltrates, confusion, uremia, low WBC or platelets, hypothermia, fluid-requiring hypotension).
Healthy outpatient CAP: high-dose amoxicillin, doxycycline, or a macrolide (if pneumococcal resistance under 25%); with comorbidities: amoxicillin-clavulanate or a cephalosporin + macrolide/doxycycline, or a respiratory fluoroquinolone alone.
Ward CAP: β-lactam + macrolide or a respiratory fluoroquinolone alone; ICU CAP: β-lactam + macrolide or fluoroquinolone (never a fluoroquinolone alone).
Atypicals (Mycoplasma, Legionella, Chlamydophila) are not covered by β-lactams; Mycoplasma = young, bullous myringitis, cold agglutinins; Legionella = water exposure, diarrhea, hyponatremia, urinary antigen.
HAP (≥48 h after admission) and VAP (≥48 h after intubation): vancomycin or linezolid plus an antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, meropenem), then de-escalate; about 7 days.
Aspiration favors the right lung (more vertical bronchus): posterior upper-lobe segments when supine, basal segments when upright; treat with amoxicillin-clavulanate or ampicillin-sulbactam.
Parapneumonic effusion with pH under 7.2, glucose under 60, high LDH, positive Gram stain, or pus needs chest tube drainage; CAP runs at least 5 days (IDSA 2019; ATS 2025 allows 3 days for nonsevere CAP once stable) and until afebrile 48–72 h and stable; corticosteroids for severe CAP only.

Diagnosis and severity scoring

Presentation. Community-acquired pneumonia (CAP) causes fever, productive cough, pleuritic chest pain, and dyspnea. The exam shows consolidation: bronchial breath sounds, egophony, dullness to percussion, and increased tactile fremitus. Older patients may present only with confusion or a fall.

Confirm with imaging. The diagnosis requires a new infiltrate on chest x-ray; symptoms and exam alone are not enough. Streptococcus pneumoniae is the most common bacterial cause. In severe CAP, and in inpatients with MRSA or Pseudomonas risk factors, send blood and sputum cultures. Pneumococcal and Legionella urinary antigen tests help in severe disease.

CURB-65. Score one point for each of the following:

Confusion
Urea: BUN >19 mg/dL
Respiratory rate ≥30
Blood pressure <90/60 (systolic <90 or diastolic ≤60 mmHg)
Age ≥65

Score 0–1Outpatient treatment.
Score 2Consider admission.
Score ≥3Admit and consider the ICU.

The Pneumonia Severity Index (PSI) is a more detailed alternative.

Who needs the ICU. Either major criterion is enough: septic shock needing vasopressors, or respiratory failure needing mechanical ventilation. Otherwise admit to the ICU for ≥3 minor criteria:

Respiratory rate ≥30 or PaO2/FiO2 ≤250
Multilobar infiltrates
Confusion or uremia
Leukopenia or thrombocytopenia
Hypothermia
Hypotension needing aggressive fluids

Empiric therapy for CAP

Empiric CAP regimens by setting

Setting	Regimen	Point to remember
Healthy outpatient	High-dose amoxicillin, or doxycycline, or a macrolide	Macrolide only where local pneumococcal resistance is <25%; no MRSA or Pseudomonas coverage
Outpatient with comorbidities	Amoxicillin-clavulanate or a cephalosporin plus a macrolide or doxycycline; or levofloxacin or moxifloxacin alone	Comorbidities: heart, lung, liver, or kidney disease, diabetes, or recent antibiotics
Inpatient (ward)	β-lactam (ceftriaxone or ampicillin-sulbactam) plus a macrolide; or a respiratory fluoroquinolone alone	Covers pneumococcus and atypicals
ICU	β-lactam plus a macrolide, or β-lactam plus a fluoroquinolone	A fluoroquinolone alone is not sufficient in the ICU

In CAP, add MRSA or antipseudomonal coverage only when specific risk factors are present, such as prior respiratory isolation of these organisms or recent hospitalization with IV antibiotics.

Duration. Treat CAP for at least 5 days (IDSA/ATS 2019); the 2025 ATS update allows a minimum of 3 days for nonsevere CAP once the patient is clinically stable. Stop only after the patient has been afebrile for 48–72 hours and is clinically stable. Extend to about 7 days for MRSA or Pseudomonas, and longer for complications such as empyema. Switch from IV to oral once the patient is improving and can take pills.

The minimum course is not an automatic stop date. Keep treating until the patient has been afebrile 48–72 hours and is stable.

Corticosteroids. The 2025 ATS update suggests systemic corticosteroids (for example hydrocortisone) for severe CAP, but not for nonsevere CAP.

Follow-up imaging. The x-ray clears weeks after the patient recovers. Consider a follow-up chest x-ray in smokers and older patients to exclude an underlying malignancy.

Atypical organisms and pathogen clues

Typical vs atypical. Typical pneumonia (pneumococcus, Klebsiella, Staphylococcus) causes lobar consolidation and high fever and responds to β-lactams. Atypical pneumonia (Mycoplasma, Legionella, Chlamydophila) causes patchy or diffuse infiltrates with prominent extrapulmonary symptoms. β-lactams do not work: Mycoplasma has no cell wall, and Legionella and Chlamydophila live inside cells. Atypicals need a macrolide, doxycycline, or a fluoroquinolone.

Mycoplasma. Young patients with "walking pneumonia": gradual dry cough, malaise, and low-grade fever. Clues are bullous myringitis and cold agglutinins (IgM that can cause hemolysis).

Legionella. High fever, diarrhea, and hyponatremia after exposure to contaminated water. Diagnose with the urinary antigen and treat with azithromycin or levofloxacin.

Legionella spreads through contaminated water systems such as cooling towers and plumbing, not from person to person.

Matching the host to the organism

Clue	Likely organism
Rust-colored sputum, lobar consolidation	Streptococcus pneumoniae
Alcoholic; currant-jelly sputum; upper-lobe disease	Klebsiella pneumoniae
Pneumonia after influenza, often necrotizing or cavitary	Staphylococcus aureus
Bronchiectasis or cystic fibrosis	Pseudomonas aeruginosa
Aspiration risk; foul-smelling sputum	Oral anaerobes
Travel or residence in endemic areas	Endemic fungi: Coccidioides (Southwest US deserts), Histoplasma (Ohio and Mississippi River valleys)

Hospital-acquired and ventilator-associated pneumonia

Definitions. Hospital-acquired pneumonia (HAP) starts ≥48 hours after admission. Ventilator-associated pneumonia (VAP) starts ≥48 hours after intubation. The old healthcare-associated pneumonia (HCAP) category has been retired, so patients from nursing homes or dialysis are judged by their individual risk factors.

Empiric regimen. Cover MRSA plus Pseudomonas and other gram-negatives:

An antipseudomonal β-lactam: piperacillin-tazobactam, cefepime, or meropenem
Plus MRSA coverage: vancomycin or linezolid
Choose agents by the patient's risk factors and the local antibiogram

De-escalate. Send respiratory cultures, ideally before antibiotics but without delaying them. Narrow therapy when cultures return, and treat for about 7 days. To help prevent VAP, raise the head of the bed and interrupt sedation daily to test readiness for extubation.

Aspiration and parapneumonic effusions

Aspiration pneumonia. Aspirated material settles in dependent segments. It favors the right lung because the right main bronchus is wider and more vertical. Position decides the segment: the posterior segments of the upper lobes (and superior segments of the lower lobes) when supine, the basal segments when upright. Risk factors are altered consciousness, dysphagia, and alcoholism. Amoxicillin-clavulanate or ampicillin-sulbactam covers the oral anaerobes. Untreated aspiration can progress to a lung abscess, a cavity with an air–fluid level.

Chemical pneumonitis (Mendelson syndrome) follows aspiration of gastric acid. It can mimic infection, but it begins as inflammation, not bacterial infection.

Parapneumonic effusion. A parapneumonic effusion can progress to empyema. Sample any effusion that is more than small (≥1 cm on a lateral decubitus film) with thoracentesis.

Uncomplicated vs complicated parapneumonic effusion

Pleural fluid	Uncomplicated	Complicated effusion or empyema
pH	≥7.2	<7.2
Glucose	≥60 mg/dL	<60 mg/dL
LDH	Lower	High
Gram stain / appearance	Negative; clear	Positive Gram stain or frank pus (empyema)
Management	Antibiotics alone	Chest tube drainage plus antibiotics

Loculated collections that drain poorly may need intrapleural fibrinolytic therapy or surgical (VATS) decortication.