Enumerate the common causes of community-acquired pneumonia in under-five children.

Common Causes of Community-Acquired Pneumonia in Under-Five Children

The causes of CAP in under-five children can be broadly categorized into viral, bacterial, and less commonly, atypical pathogens. The relative importance of each varies with the child’s age and immune status.

1. Viral Causes

• Respiratory Syncytial Virus (RSV): The most common viral cause, particularly in infants under six months of age. Often causes bronchiolitis, which can progress to pneumonia.
• Rhinovirus: A frequent cause, especially in older infants and toddlers.
• Influenza Virus (A & B): More common during seasonal epidemics. Can cause severe pneumonia, especially in children with underlying medical conditions.
• Adenovirus: Can cause a range of respiratory illnesses, including pneumonia, often with associated conjunctivitis.
• Parainfluenza Virus: Frequently causes croup, but can also lead to pneumonia.
• Human Metapneumovirus (hMPV): Similar to RSV in clinical presentation and epidemiology.

2. Bacterial Causes

• Streptococcus pneumoniae (Pneumococcus): The most common bacterial cause overall, particularly in children aged 6 months to 5 years.
• Haemophilus influenzae type b (Hib): Historically a major cause, but incidence has decreased significantly with widespread Hib vaccination. Still relevant in unvaccinated populations.
• Mycoplasma pneumoniae: More common in school-aged children, but can occur in older preschoolers. Causes atypical pneumonia.
• Chlamydophila pneumoniae: Another cause of atypical pneumonia, less common than Mycoplasma pneumoniae.
• Staphylococcus aureus: Increasingly recognized as a cause, particularly after influenza infection or in children with underlying lung disease.
• Moraxella catarrhalis: Common in children with otitis media and can cause pneumonia.

3. Age-Specific Etiology

Age Group	Common Causes
Infants (<6 months)	RSV, Rhinovirus, Adenovirus, Streptococcus pneumoniae, Chlamydia trachomatis (consider congenital pneumonia)
6 months – 2 years	RSV, Rhinovirus, Streptococcus pneumoniae, Haemophilus influenzae type b (in unvaccinated), Mycoplasma pneumoniae (less common)
2 – 5 years	Rhinovirus, Influenza, Streptococcus pneumoniae, Mycoplasma pneumoniae, Chlamydophila pneumoniae

4. Other Considerations

• Aspiration: Especially in infants with gastroesophageal reflux or neurological impairment.
• Foreign Body Aspiration: Can lead to localized pneumonia.
• Immunodeficiency: Children with underlying immunodeficiencies are at increased risk of severe and recurrent pneumonia.

Diagnosis typically involves clinical assessment, chest radiography, and sometimes blood cultures or respiratory viral panels. Prompt and appropriate antibiotic therapy is crucial for bacterial pneumonia, while supportive care is the mainstay of treatment for viral pneumonia.