Definition And Epidemiology

• Community acquired pneumonia represents an acute infection of the lung parenchyma.
• It occurs in previously healthy children and is acquired outside of hospital settings.
• The definition excludes children hospitalized within 14 days prior to symptom onset.
• It excludes patients with immunodeficiency, severe malnutrition, and post-measles states.
• It acts as the leading infectious cause of death globally in children under five years of age.
• Mortality is closely linked to poverty, with over 99% of deaths occurring in low and middle-income nations.
• Incidence has declined due to widespread use of antibiotics and vaccines.
• Key protective vaccines include measles, pertussis, Haemophilus influenzae type b (Hib), and pneumococcal conjugate vaccine (PCV).

Pathogenesis And Anatomical Classification

• The disease begins with the disruption of the complex lower respiratory ecosystem.
• Pathogens typically enter via droplet infection.
• Viral infections spread along the respiratory epithelium.
• This leads to airway obstruction from swelling, abnormal secretions, and cellular debris.
• Bacterial pathogens multiply directly within the alveoli.
• This multiplication produces an inflammatory exudate leading to alveolar consolidation.
• Anatomical classification includes lobar pneumonia, lobular pneumonia (bronchopneumonia), and interstitial pneumonia.

Etiological Profile

Age-Specific Pathogens

Exposure-Specific Pathogens

Clinical Presentation

Symptomatology And Signs

• The illness often begins with an upper respiratory tract infection prodrome featuring rhinitis and cough.
• Tachypnea serves as the most consistent and sensitive clinical manifestation.
• Respiratory distress is evidenced by intercostal, subcostal, or suprasternal retractions.
• Accessory muscle use, nasal flaring, and grunting may be present.
• Auscultation frequently reveals crackles, wheezing, bronchial breathing, and diminished air entry.
• Severe disease manifests with cyanosis, lethargy, tachycardia, and hypoxemia.
• Patients may complain of abdominal pain due to referred pain from lower lobe involvement.

World Health Organization Tachypnea Criteria

Differentiating Pneumonia Syndromes

Triaging And Admission Criteria

• Assess airway, breathing, and circulation upon arrival.
• Hospitalization is indicated for any infant under three to six months of age.
• Admit patients exhibiting hypoxemia, defined as oxygen saturation below 90-92% on room air.
• Admit children demonstrating a toxic appearance, lethargy, or unconsciousness.
• Severe respiratory distress, intermittent apnea, and grunting mandate admission.
• Inability to tolerate oral fluids or feed, persistent vomiting, and severe dehydration require inpatient care.
• Presence of complicated pneumonia, such as effusion, empyema, or abscess, requires admission.
• Failure of outpatient therapy within 48 to 72 hours warrants hospitalization.

Diagnostic Evaluation

Laboratory Investigations

• Community acquired pneumonia is primarily a clinical diagnosis.
• Routine investigations are not required in an outpatient setting.
• Hospitalized children require a complete blood count and blood cultures.
• Viral infections typically show a normal or slightly elevated white blood cell count ($\le$ 20,000/mm³) with lymphocyte predominance.
• Bacterial etiologies yield white blood cell counts of 15,000 to 40,000/mm³ with polymorphonuclear predominance.
• Inflammatory markers like C-reactive protein and procalcitonin are elevated in bacterial disease and aid in monitoring treatment response.
• Molecular multiplex reverse transcription polymerase chain reaction panels identify specific viral pathogens.
• Isotype enzyme linked immunosorbent assay is superior to cold agglutinins for Mycoplasma detection.
• Pulse oximetry remains essential for assessing severity and monitoring therapy.

Imaging Modalities

• Routine chest radiographs are not required for uncomplicated outpatient cases.
• Radiographs identify consolidation, atelectasis, hyperinflation, and pleural effusions.
• The presence of pneumatoceles suggests Staphylococcus or Klebsiella infections.
• Chest ultrasonography serves as a highly sensitive point of care tool to identify consolidations and effusions.
• Contrast enhanced computed tomography provides superior imaging for identifying necrosis, abscesses, or underlying anatomical defects.

Differential Diagnosis

• Recurrent pneumonia should be considered if there are $\ge$ 2 episodes per year or $\ge$ 3 episodes in a lifetime with radiographic clearing between episodes.
• Hereditary causes include cystic fibrosis and sickle cell disease.
• Immunodeficiency disorders like HIV, chronic granulomatous disease, and severe combined immunodeficiency present similarly.
• Ciliary disorders such as primary ciliary dyskinesia should be excluded.
• Anatomic malformations include pulmonary sequestration and congenital pulmonary airway malformations.
• Acquired causes include retained foreign bodies and severe gastroesophageal reflux disease.

Management Strategies

Outpatient Pharmacotherapy

Inpatient Pharmacotherapy

General Inpatient Protocol

Supportive Care

• Provide continuous oxygen therapy to maintain oxygen saturation above 94%.
• Administer intravenous fluids to address severe distress or clinical dehydration.
• Use Paracetamol as an antipyretic for fever control and comfort.
• Provide advanced respiratory support such as bubble continuous positive airway pressure, high flow nasal cannula, or mechanical ventilation for impending respiratory failure.

Complications

• Local and intrathoracic complications include pleural effusion, empyema, and pyopneumothorax.
• Pneumatocele formation, lung abscess, necrotizing pneumonia, and bronchopleural fistulas may occur.
• Systemic and metastatic complications encompass bacteremia and overwhelming sepsis.
• Infection may seed to remote locations causing purulent pericarditis, meningitis, suppurative arthritis, and osteomyelitis.

Prevention Strategies

• Timely immunization remains the most effective preventive measure.
• Ensure administration of pneumococcal conjugate vaccine, Haemophilus influenzae type b vaccine, influenza vaccine, measles vaccine, and pertussis vaccine.
• High-risk infants may receive Nirsevimab for passive immunoprophylaxis against respiratory syncytial virus.
• Environmental measures include promoting exclusive breastfeeding and preventing exposure to passive tobacco smoke.
• Addressing household crowding and providing adequate zinc supplementation significantly mitigates disease risk.