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RespiratoryICD-10: J18About 1.5 million emergency department visits annually in the US; leading infectious cause of death in children worldwide

Pneumonia

Also known as: Lung Infection

Pneumonia is an infection of the lungs that inflames the air sacs (alveoli), causing them to fill with fluid or pus. It can be caused by bacteria, viruses, or fungi, and ranges from mild to life-threatening, particularly in infants, older adults, and people with weakened immune systems. Pneumonia is the leading infectious cause of death in children worldwide and a common reason for hospitalization in adults.

Symptoms

Cough, often producing green, yellow, or bloody mucus
High fever, sweating, and shaking chills
Shortness of breath, even at rest
Chest pain that worsens with breathing or coughing
Fatigue and weakness
Nausea, vomiting, or diarrhea
Confusion (especially in older adults)
Low body temperature (in older adults or immunocompromised individuals)

Causes

  • Bacterial infection (Streptococcus pneumoniae most common; also Mycoplasma, Legionella, Staphylococcus)
  • Viral infection (influenza, RSV, SARS-CoV-2, adenovirus)
  • Fungal infection (Pneumocystis, Histoplasma — especially in immunocompromised)
  • Aspiration of food, liquid, or vomit into the lungs

Risk Factors

  • Age under 2 or over 65
  • Chronic lung disease (COPD, asthma)
  • Smoking
  • Weakened immune system (HIV, chemotherapy, organ transplant)
  • Hospitalization (especially on mechanical ventilation)
  • Chronic diseases (heart disease, diabetes, liver or kidney disease)

Diagnosis

  • Chest X-ray showing pulmonary infiltrate
  • Physical examination (crackles, decreased breath sounds, dullness to percussion)
  • Sputum culture and Gram stain
  • Blood cultures
  • CT scan for complicated or non-responding cases

Treatment

  • Antibiotics for bacterial pneumonia (amoxicillin, azithromycin, fluoroquinolones depending on severity)
  • Antiviral agents for influenza pneumonia (oseltamivir) or COVID-19 pneumonia
  • Supportive care: rest, fluids, oxygen supplementation as needed
  • Hospitalization and IV antibiotics for severe community-acquired pneumonia
  • Mechanical ventilation for respiratory failure

Prevention

  • Pneumococcal vaccination (PCV15 or PCV20)
  • Annual influenza vaccination
  • COVID-19 vaccination
  • Good hand hygiene and respiratory etiquette
  • Smoking cessation

When to See a Doctor

  • Persistent cough with fever and difficulty breathing
  • Chest pain with breathing
  • Symptoms not improving or worsening after 48 hours of antibiotics
  • High-risk individual (elderly, immunocompromised, chronic disease) with respiratory symptoms

Frequently Asked Questions

Related Conditions

Influenza

Infectious

Bronchitis

Respiratory

Pertussis

Infectious

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Medical Disclaimer: This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.

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