Community-acquired pneumonia accounts for approximately 1.4 million ED visits, 740,000 hospitalizations, and 41,000 deaths annually in the US. [1] It is defined as pneumonia acquired outside the hospital setting (or >48 hours before admission) and now includes patients previously classified as having "health care–associated pneumonia". [1]
1. History
- Cough (often productive), dyspnea, pleuritic chest pain, and fever/chills are hallmark symptoms [2-3]
- Characterize onset (acute vs subacute), sputum color/quantity, hemoptysis, and severity of dyspnea
- Timing: symptom duration, preceding URI, recent travel, sick contacts, animal/environmental exposures
- Associated symptoms: myalgias, rigors, night sweats, nausea/vomiting, confusion (especially elderly)
- Important negatives: absence of abnormal vital signs has good negative predictive value for ruling out CAP (sensitivity 93%, negative LR 0.25) [1]
- Elderly and immunocompromised patients may present without classic symptoms — atypical presentations (confusion, falls, functional decline) are common [2]
2. Alarm Features
- Respiratory rate ≥30, SpO₂ <90%, systolic BP <90 mmHg, new-onset confusion
- Multilobar infiltrates on imaging
- Hypothermia (core temp <36°C) — paradoxically associated with worse prognosis
- Leukopenia (WBC <4,000/μL), thrombocytopenia (<100,000/μL), BUN ≥20 mg/dL [2][4]
- ATS/IDSA major criteria for severe CAP: need for mechanical ventilation or septic shock requiring vasopressors — meeting 1 major or ≥3 minor criteria defines severe CAP [2][4]
- Rapid clinical deterioration, inability to maintain oral intake, hemoptysis, cavitary lesion
3. Medications
Medications that increase CAP risk
- Inhaled corticosteroidsatypical antipsychoticsPPIs[5-7]
Treatment medications (see Treatment Plan below for full details):
- Outpatient without comorbidities: amoxicillin 1 g TID or doxycycline 100 mg BID [1][4]
- Outpatient with comorbidities: amoxicillin-clavulanate or cephalosporin + macrolide; or respiratory fluoroquinolone monotherapy [4]
- Inpatient nonsevere: ceftriaxone + azithromycin (preferred) or respiratory fluoroquinolone [1]
- Severe CAP: β-lactam + macrolide + corticosteroids (hydrocortisone 200 mg/day IV or equivalent) [1][8]
Contraindicated/caution medications
- Macrolides and fluoroquinolones can prolong QTc — avoid in patients with baseline prolonged QT, concurrent QT-prolonging drugs, or uncorrected hypokalemia/hypomagnesemia [4][9]
- Metronidazole and clindamycin should NOT be added empirically for aspiration coverage — associated with 5–6% higher mortality and increased C. difficile risk [1]
- Fluoroquinolones carry risks of tendon rupture, C. difficile, and aortic dissection — reserve for β-lactam intolerance [1]
4. Diet
- Maintain adequate oral hydration; dehydration worsens mucociliary clearance and can concentrate BUN (affecting severity scoring)
- Ensure adequate caloric intake — hypoalbuminemia is an independent risk factor for poor outcomes [6]
- No specific dietary triggers; however, aspiration risk should be assessed in patients with dysphagia, altered mental status, or alcohol use
- Long-term: optimize nutrition in elderly and chronically ill patients to reduce recurrence risk
5. Review of Systems
- Pulmonary: cough, sputum production, hemoptysis, dyspnea, wheezing, pleuritic chest pain
- Cardiovascular: chest pain, palpitations, leg swelling (CVEs complicate ~32% of hospitalized CAP) [10]
- Neurologic: confusion, headache (Legionella), altered mental status
- GI: nausea, vomiting, diarrhea (common with Legionella, also assess aspiration risk)
- Musculoskeletal: myalgias (viral or atypical pathogens)
- Constitutional: fever, chills, rigors, night sweats, weight loss (consider TB, malignancy)
6. Collateral History and Family History
- Collateral: baseline functional status, recent hospitalizations or antibiotic use (within 90 days — risk factor for resistant organisms), nursing home residence, vaccination status (pneumococcal, influenza, COVID-19)
- Exposure history: sick contacts, travel (Legionella, Coccidioides, Histoplasma), animal contact (psittacosis, Q fever), occupational exposures
- Family history: immunodeficiency syndromes, alpha-1 antitrypsin deficiency, cystic fibrosis (if recurrent pneumonias in younger patients)
- Social context: smoking, alcohol use, homelessness, substance use, ability to comply with outpatient therapy [4]
7. Risk Factors
- Age ≥65 years — incidence 63.0 per 10,000 person-years vs 24.8 overall [1]
- Smoking (active and passive in elderly) [11]
- Chronic lung disease (COPD, asthma, bronchiectasis)
- Immunosuppression: HIV, chemotherapy, organ transplant, chronic corticosteroid use
- Chronic heart, liver, or renal disease; diabetes mellitus; alcoholism; malignancy; asplenia [4]
- Recent hospitalization and parenteral antibiotics within 90 days (risk for MRSA/Pseudomonas) [1]
- Poor dental hygiene, dysphagia, impaired consciousness (aspiration risk) [11]
- Medications: inhaled corticosteroids, PPIs, antipsychotics [5]
8. Differential Diagnosis
- Acute bronchitis — no infiltrate on imaging, self-limited
- COPD/asthma exacerbation — wheezing predominant, may overlap with CAP
- Pulmonary embolism — pleuritic chest pain, dyspnea, risk factors for VTE; CT angiography distinguishes
- Heart failure/pulmonary edema — bilateral infiltrates, elevated BNP, orthopnea, peripheral edema
- Aspiration pneumonitis — chemical injury without infection; distinguish from aspiration pneumonia
- Lung malignancy — mass-like opacity, persistent infiltrate despite antibiotics, weight loss, hemoptysis
- Tuberculosis — subacute course, upper lobe cavitary disease, risk factors (immigration, HIV, incarceration)
- COVID-19 / Influenza — viral pneumonia with bilateral ground-glass opacities; test during community transmission [1]
9. Past Medical History
- Prior pneumonia episodes (frequency, pathogens, hospitalizations)
- Prior respiratory isolates of MRSA or Pseudomonas — critical for antibiotic selection [1]
- Chronic lung disease, heart failure, CKD, liver disease, diabetes, malignancy
- Immunosuppressive conditions or medications
- Surgical history: splenectomy (encapsulated organism risk), thoracic surgery
- Vaccination history: PCV20 (or PCV15 + PPSV23), influenza, COVID-19 [12]
10. Physical Exam
Vital signs
- hypoxemia (SpO₂ <90%)[3-4]
Focused lung exam
- Egophony — specificity 99% for CAP (uncommon but highly specific) [1]
- Dullness to percussion — specificity 94% [1]
- Crackles/rales, rhonchi, decreased breath sounds — mixed sensitivity/specificity [1]
- Tactile fremitus, whispered pectoriloquy (signs of consolidation) [3]
Other
- Mental status assessment (confusion = CURB-65 criterion)
- Signs of volume overload (JVD, peripheral edema — consider heart failure)
- Skin exam for signs of sepsis (mottling, delayed capillary refill)
- Normal lung exam has good negative predictive value for ruling out CAP [3]
11. Lab Studies
Recommended for all hospitalized patients
- CBC with differential — leukocytosis (>10,000) or leukopenia (<4,000) [2]
- BMP — BUN (severity scoring), creatinine, electrolytes
- Procalcitonin — elevated in bacterial CAP, low in viral; NPV 98.3% for bacterial coinfection at ≤0.1 ng/mL; however, can be falsely negative with atypical bacteria (Mycoplasma) and falsely positive in renal injury [13]
- Lactate — if sepsis suspected
- COVID-19 and influenza testing — recommended for all patients when viruses are circulating [1]
Recommended for severe CAP or MRSA/Pseudomonas risk factors:
- Blood cultures (2 sets before antibiotics) [1]
- Sputum Gram stain and culture [13]
- MRSA nasal swab — 99% NPV if negative; useful for de-escalation [1]
- Pneumococcal urinary antigen — only changes management if anti-MRSA/Pseudomonas therapy started [1]
- Legionella urinary antigen — detects only L. pneumophila serogroup 1 [1]
Not routinely recommended
The following table from the 2024 JAMA review summarizes diagnostic testing recommendations:
12. Imaging
First-line: Chest radiograph (PA and lateral)
- Air space opacities/infiltrates are the most common finding (>95%) [1]
- Sensitivity is limited (median 70%, range 16–95%) — only 43.5% of CT-visible opacities are seen on CXR [1]
- Pleural effusion (especially unilateral/loculated), cavitation, and mass-like appearance are less common but important findings
CT chest
- Indicated when CXR is negative but clinical suspicion remains high [1][13]
- Better for alternative diagnoses (PE, malignancy, empyema)
- Gold standard sensitivity for parenchymal disease
Lung ultrasound
- Higher sensitivity (median 95%) and specificity (median 75%) than CXR when performed by trained operators [1-2]
- Dynamic air bronchograms are considered pathognomonic for pneumonia on ultrasound [2]
- ATS 2025 guidelines recognize lung ultrasound as an acceptable alternative when expertise is available [2]
When imaging is unnecessary
- Follow-up imaging is NOT recommended if symptoms resolve within 5–7 days [2]
- Follow-up CXR at 4–6 weeks is suggested for patients with persistent symptoms, smokers, or those at risk for lung cancer [2][13]
13. Special Tests
Severity scoring systems
- PSI (Pneumonia Severity Index) — preferred by ATS/IDSA for site-of-care decisions; classes I–III are low risk and can be treated outpatient [4]
- CURB-65 — simpler; score 0–1 = outpatient, 2 = consider short stay/observation, 3–5 = hospitalize [13]
- ATS/IDSA Severe CAP Criteria — 1 major or ≥3 minor criteria = severe CAP requiring ICU [4]
- SMART-COP — predicts need for vasopressors/mechanical ventilation [3]
Point-of-care tests
- Rapid influenza/COVID-19 antigen or PCR
- Point-of-care lung ultrasound
- MRSA nasal PCR
Procedures
- Thoracentesis — if significant pleural effusion; rule out empyema/complicated parapneumonic effusion (pH, glucose, LDH, cell count, Gram stain, culture)
- Bronchoscopy with BAL — rarely indicated in CAP; consider if immunocompromised, treatment failure, or concern for opportunistic infection (PJP, TB) [1][14]
14. ECG
- Obtain a 12-lead ECG on all hospitalized CAP patients, particularly those with pre-existing cardiac disease, older age, or severe pneumonia [9]
- New-onset atrial fibrillation occurs in ~7.6–9.5% of hospitalized CAP patients and is associated with increased mortality [15-16]
- Cardiovascular events (heart failure, arrhythmia, MI) complicate ~32% of hospitalized CAP cases, with >50% occurring within the first 24 hours [9-10]
- Monitor QTc interval — both macrolides (azithromycin, clarithromycin) and fluoroquinolones (levofloxacin, moxifloxacin) can prolong QT [9][17]
- Watch for: sinus tachycardia, new AF, ST changes (ischemia), right heart strain pattern (if PE considered)
15. Assessment
Severity stratification is the cornerstone of CAP management and drives site-of-care and treatment decisions:
- Outpatient (PSI I–III or CURB-65 0–1): 30-day mortality <1% [3]
- Inpatient nonsevere: PSI IV or CURB-65 2; 30-day mortality ~9% [3]
- Inpatient severe (PSI V or ATS/IDSA severe criteria): 30-day mortality up to 27% [3]
Typical presentation is acute onset of cough, fever, and dyspnea with a radiographic infiltrate. Atypical presentations (afebrile, minimal cough, confusion only) are common in elderly and immunocompromised patients. [2] Only 38% of hospitalized patients have a pathogen identified; of those, up to 40% are viral. [1]
Complications to consider: sepsis, ARDS, empyema/parapneumonic effusion, lung abscess, cardiovascular events (MI, new AF, heart failure), and post-pneumonia long-term sequelae. [2][10]
16. Treatment Plan
Initial stabilization
- Supplemental O₂ to maintain SpO₂ ≥92% (≥88% in COPD)
- IV fluid resuscitation if hypotensive/septic
- Administer antibiotics as early as possible
Empiric antibiotic therapy (per 2019 ATS/IDSA guidelines): [1][4]
Duration
- Minimum 3 days for nonsevere CAP with rapid clinical stabilization (afebrile, HR <100, RR <24, SpO₂ ≥90%, SBP ≥90, able to eat) by day 3 [1]
- 5 days for patients who take longer to stabilize [1]
- ≥7 days for MRSA, Pseudomonas, empyema, or complicated infections [1]
Corticosteroids in severe CAP
- Hydrocortisone 200 mg/day IV (continuous infusion or divided doses) for 4–7 days, initiated within 24 hours of meeting severity criteria, reduces 28-day mortality by ~5.6% (CAPE COD trial) [1][8]
- Not recommended for nonsevere CAP [1]
Antivirals
17. Disposition
Discharge criteria (outpatient treatment)
- PSI class I–III or CURB-65 0–1
- Able to tolerate oral medications and maintain oral intake
- Adequate home support and ability to follow up
- No hypoxemia on room air, hemodynamically stable [4][13]
Admission criteria
- PSI class IV–V or CURB-65 ≥3
- Hypoxemia requiring supplemental O₂
- Inability to tolerate oral medications
- Unstable comorbidities, altered mental status
- Social factors: homelessness, substance use, no reliable follow-up [4]
ICU admission
Observation
Specialist consultation triggers
- Pulmonology: treatment failure, cavitary lesion, recurrent pneumonia, empyema requiring drainage
- Infectious disease: resistant organisms, immunocompromised host, unusual pathogens
- Cardiology: new arrhythmia, acute coronary syndrome, decompensated heart failure [9]
18. Follow Up / Return Precautions
Follow-up timing
- Outpatients: follow-up within 48–72 hours if not improving, or within 1–2 weeks for reassessment
- Post-discharge: early outpatient follow-up (within 1–2 weeks) reduces readmission risk [13]
- Follow-up CXR at 4–6 weeks only if persistent symptoms, smoker, or age/risk factors for malignancy [2][13]
Return precautions — instruct patients to return immediately for:
- Worsening shortness of breath or inability to breathe comfortably at rest
- High fever (>39°C/102.2°F) persisting >48 hours on antibiotics or new fever after initial improvement
- Chest pain, palpitations, lightheadedness, or syncope
- Confusion or altered mental status
- Inability to keep down fluids or medications
- Hemoptysis or coughing up blood
Expected recovery course
- Fever typically resolves within 2–4 days of appropriate antibiotics
- Cough and fatigue may persist for 2–6 weeks even with successful treatment
- Full radiographic resolution may take 6–8 weeks, especially in elderly or those with comorbidities [2]
Patient counseling
- Complete the prescribed antibiotic course (even if feeling better)
- Ensure pneumococcal, influenza, and COVID-19 vaccinations are up to date [12]
- Smoking cessation counseling
- Cardiovascular risk remains elevated for weeks to months post-CAP — monitor for new cardiac symptoms [2]
References
1. Community-Acquired Pneumonia: A Review. — Vaughn VM, Dickson RP, Horowitz JK, Flanders SA. The Journal of the American Medical Association. 2024.
2. Community-Acquired Pneumonia. — Reyes LF, Conway Morris A, Serrano-Mayorga C, et al. Lancet. 2025.
3. Community-Acquired Pneumonia in Adults. — Bai AD, Loeb M. NEJM Evidence. 2025.
4. Diagnosis and Treatment of Adults With Community-Acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. — Metlay JP, Waterer GW, Long AC, et al. American Journal of Respiratory and Critical Care Medicine. 2019.
5. Drugs That Increase the Risk of Community-Acquired Pneumonia: A Narrative Review. — Liapikou A, Cilloniz C, Torres A. Expert Opinion on Drug Safety. 2018.
6. Pharmacotherapy and the Risk for Community-Acquired Pneumonia. — Gau JT, Acharya U, Khan S, et al. BMC Geriatrics. 2010.
7. Proton Pump Inhibitors and the Risk of Community-Acquired Pneumonia: An Updated Meta-Analysis. — Xun X, Yin Q, Fu Y, He X, Dong Z. The Annals of Pharmacotherapy. 2022.
8. Low-Dose Corticosteroids for Critically Ill Adults With Severe Pulmonary Infections: A Review. — Pirracchio R, Venkatesh B, Legrand M. The Journal of the American Medical Association. 2024.
9. Acute Pneumonia and the Cardiovascular System. — Corrales-Medina VF, Musher DM, Shachkina S, Chirinos JA. Lancet. 2013.
10. Cardiovascular Complications and Short-Term Mortality Risk in Community-Acquired Pneumonia. — Violi F, Cangemi R, Falcone M, et al. Clinical Infectious Diseases : An Official Publication of the Infectious Diseases Society of America. 2017.
11. New Evidence of Risk Factors for Community-Acquired Pneumonia: A Population-Based Study. — Almirall J, Bolíbar I, Serra-Prat M, et al. The European Respiratory Journal. 2008.
12. Community-Acquired Pneumonia in Adults: Rapid Evidence Review. — Womack J, Kropa J. American Family Physician. 2022.
13. Community-Acquired Pneumonia. — File TM, Ramirez JA. The New England Journal of Medicine. 2023.
14. Guidelines for the Prevention and Treatment of Opportunistic Infections in Adults and Adolescents With HIV. — Constance Benson, John Brooks, Shireesha Dhanireddy, et al Infectious Diseases Society of America; Office of AIDS Research Advisory Council (2025). 2025.
15. Left Atrium Dilatation and Left Ventricular Hypertrophy Predispose to Atrial Fibrillation in Patients With Community-Acquired Pneumonia. — Cangemi R, Calvieri C, Taliani G, et al. The American Journal of Cardiology. 2019.
16. Prevalence of New-Onset Atrial Fibrillation in Hospitalized Patients With Community-Acquired Pneumonia: A Systematic Review and Meta-Analysis. — Corica B, Tartaglia F, Oliva A, et al. Internal and Emergency Medicine. 2023.
17. Update to Practice Standards for Electrocardiographic Monitoring in Hospital Settings: A Scientific Statement From the American Heart Association. — Sandau KE, Funk M, Auerbach A, et al. Circulation. 2017.