Community‑Acquired Pneumonia (CAP)

Overview

Community‑acquired pneumonia (CAP) is an infection of the lung tissue that develops in people who have not been recently hospitalized or lived in a long‑term care facility. It is the most common type of pneumonia and a leading cause of infectious death worldwide.

• Who it affects: CAP can occur at any age, but incidence rises sharply after age 65 and in young children (<5 years). Men and women are affected equally, though certain risk groups (e.g., smokers, persons with chronic diseases) see higher rates.
• Prevalence: In the United States, there are about 5–6 million episodes of CAP each year, resulting in >1 million hospital admissions and ~50,000 deaths (CDC, 2023). Globally, the WHO estimates ~150 million cases annually.
• Seasonality: Cases peak in the winter months in temperate climates, coinciding with higher circulation of respiratory viruses.

Symptoms

Symptoms can range from mild to severe and often overlap with other respiratory infections. Typical features include:

• Fever or chills – often >38 °C (100.4 °F).
• Cough – may produce sputum that is purulent (yellow/green), rust‑colored, or blood‑tinged.
• Shortness of breath (dyspnea) – especially on exertion or when lying flat.
• Chest pain – pleuritic pain that worsens with deep breathing or coughing.
• Fatigue and malaise – generalized weakness that can last weeks.
• Headache and muscle aches – common when a viral infection precedes bacterial superinfection.
• Confusion or altered mental status – more frequent in older adults.
• Loss of appetite, nausea, or vomiting – especially in children.

Causes and Risk Factors

Microbial causes

CAP is most often bacterial, but viruses and atypical organisms also play a role.

Category	Common Pathogens
Typical bacteria	Streptococcus pneumoniae (most common), Haemophilus influenzae, Moraxella catarrhalis, Staphylococcus aureus (including MRSA), Klebsiella pneumoniae
Atypical bacteria	Legionella pneumophila, Mycoplasma pneumoniae, Chlamydophila pneumoniae
Viruses	Influenza, respiratory syncytial virus (RSV), human metapneumovirus, SARS‑CoV‑2, adenovirus

Risk factors

• Age ≥ 65 years – immune senescence reduces defense.
• Chronic lung disease – COPD, asthma, bronchiectasis.
• Cardiovascular disease, diabetes, chronic kidney disease.
• Smoking or exposure to second‑hand smoke.
• Alcohol misuse – impairs cough reflex and mucociliary clearance.
• Immunosuppression – HIV/AIDS, organ transplantation, chemotherapy, biologic agents.
• Recent viral upper‑respiratory infection – predisposes to bacterial superinfection.
• Living in crowded settings – shelters, dormitories, prisons.

Diagnosis

Accurate diagnosis blends clinical assessment with targeted investigations.

Clinical evaluation

• History (onset, exposures, comorbidities).
• Physical exam – tachypnea, crackles, egophony, decreased breath sounds.
• Severity scoring (e.g., CURB‑65, PSI) to guide outpatient vs. inpatient treatment.

Laboratory and imaging studies

• Chest X‑ray – first‑line; shows lobar or patchy infiltrates in >90 % of adults.
• Blood tests – CBC (often neutrophilic leukocytosis), C‑reactive protein (CRP) or procalcitonin to gauge bacterial infection.
• Sputum Gram stain & culture – useful when good‑quality sputum is produced.
• Blood cultures – recommended for severe CAP or if MRSA/gram‑negative sepsis is suspected.
• Urinary antigen tests for S. pneumoniae and L. pneumophila (rapid, high specificity).
• Viral PCR panel (nasopharyngeal swab) – especially during flu season or pandemics.
• CT scan – reserved for complicated cases, atypical presentations, or when X‑ray is inconclusive.

Treatment Options

Antibiotic therapy

Choice depends on suspected pathogen, severity, recent antibiotic exposure, and local resistance patterns.

• Outpatient, no comorbidities –
  • Amoxicillin 1 g PO BID for 5–7 days, or
  • Doxycycline 100 mg PO BID for 5 days.
• Outpatient, comorbidities or recent antibiotics –
  • Combination therapy: e.g. amoxicillin‑clavulanate + macrolide (azithromycin) OR
  • Respiratory fluoroquinolone (levofloxacin 750 mg PO daily) for 5 days.
• Inpatient, non‑ICU –
  • β‑lactam (ceftriaxone 1–2 g IV q24h) + macrolide, or
  • Respiratory fluoroquinolone monotherapy.
• Inpatient, ICU –
  • Broad‑spectrum β‑lactam (cefepime, piperacillin‑tazobactam) + azithromycin,
  • Consider MRSA coverage (vancomycin or linezolid) if risk factors present,
  • Consider atypical coverage (levofloxacin).

Adjunctive therapies

• Oxygen supplementation to maintain SpO₂ ≥ 94 % (≥ 90 % in COPD).
• Intravenous fluids for dehydration, but avoid overload.
• Corticosteroids – low‑dose dexamethasone may reduce mortality in severe CAP (RECOVERY trial, 2021).
• Vaccination – influenza and pneumococcal vaccines reduce future episodes.

Lifestyle and supportive care

• Rest, hydration, and gradual return to activity.
• Bronchodilators for patients with underlying COPD or asthma.
• Smoking cessation and avoidance of alcohol excess.

Living with Community‑Acquired Pneumonia

Self‑care during recovery

• Medication adherence – complete the full antibiotic course, even if feeling better.
• Hydration – sip water, broths, or electrolyte solutions 2–3 L/day unless fluid‑restricted.
• Nutrition – protein‑rich foods (lean meat, beans, dairy) support immune repair.
• Breathing exercises – incentive spirometry or deep‑breathing repetitions every 2‑3 hours while awake.
• Activity pacing – start with short walks; avoid heavy lifting for 2‑3 weeks.

Monitoring & follow‑up

• Re‑evaluate with a clinician if fever persists >48 h after starting antibiotics.
• Repeat chest X‑ray 2–3 weeks after discharge for smokers or those with comorbid lung disease.
• Discuss vaccination updates before returning to normal activities.

Prevention

• Vaccination –
  • Pneumococcal conjugate (PCV13) and polysaccharide (PPSV23) per CDC schedule.
  • Annual influenza vaccine; consider high‑dose or adjuvanted formulations for >65 y.
• Hand hygiene – wash hands with soap ≥20 seconds or use alcohol‑based sanitizer.
• Respiratory etiquette – cover mouth/nose when coughing, avoid close contact with sick individuals.
• Smoking cessation – reduces mucociliary dysfunction and bacterial colonization.
• Manage chronic conditions – optimal control of diabetes, heart disease, and COPD lowers risk.
• Avoid excessive alcohol and illicit drug use, both of which impair immune defenses.

Complications

If untreated or inadequately treated, CAP can lead to serious, sometimes life‑threatening sequelae:

• Respiratory failure – need for mechanical ventilation.
• Septic shock – multi‑organ dysfunction requiring ICU care.
• Pleural empyema – collection of pus in the pleural space; may need drainage.
• Abscess formation – especially with Staphylococcus aureus.
• Acute respiratory distress syndrome (ARDS).
• Cardiac events – myocardial infarction or arrhythmias precipitated by systemic inflammation.
• Long‑term functional decline – particularly in elderly patients; may result in loss of independence.

When to Seek Emergency Care

If you or a loved one experiences any of the following, call 911 or go to the nearest emergency department immediately:

• Difficulty breathing or shortness of breath at rest.
• Chest pain that is severe, sharp, or radiates to the arm, jaw, or back.
• Persistent high fever (>39 °C / 102 °F) or fever that does not improve after 48 hours of antibiotics.
• New confusion, agitation, or a sudden change in mental status.
• Blue‑tinged lips or fingernails (cyanosis).
• Rapid heart rate (>130 bpm) or very low blood pressure (systolic <90 mmHg).
• Severe cough producing blood‑tinged sputum.
• Worsening symptoms after initial improvement (possible relapse).

References

• Centers for Disease Control and Prevention (CDC). Pneumonia & COVID‑19. Updated 2023.
• Mayo Clinic. Community‑acquired pneumonia. Accessed May 2024.
• National Institutes of Health – National Heart, Lung, and Blood Institute. Pneumonia. 2022.
• World Health Organization. Pneumonia fact sheet. 2023.
• Cleveland Clinic. Pneumonia. Reviewed 2024.
• Mandell LA, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community‑Acquired Pneumonia. Clin Infect Dis. 2019.
• RECOVERY Collaborative Group. Dexamethasone in Hospitalized Patients with COVID‑19. N Engl J Med. 2021;384:693‑704.