What are the differential diagnoses for a pediatric or geriatric patient presenting with symptoms suggestive of Pneumococcal Community-Acquired Pneumonia (PCAP)?

Differential Diagnoses for Pediatric Community-Acquired Pneumonia

When evaluating a child with suspected pneumococcal community-acquired pneumonia (PCAP), the primary differential diagnoses include viral pneumonia (particularly RSV, influenza, parainfluenza, rhinovirus, and adenovirus), atypical bacterial pneumonia (Mycoplasma pneumoniae, Chlamydophila pneumoniae), other bacterial pneumonias (non-pneumococcal), and non-infectious respiratory conditions that can mimic pneumonia. 1, 2

Infectious Differential Diagnoses

Viral Pneumonia

• Respiratory syncytial virus (RSV) is the most common viral etiology, representing up to 40% of identified pathogens in children with CAP, particularly in those under 2 years of age 1, 2
• Parainfluenza, rhinovirus, influenza, and adenovirus are other frequent viral causes, with respiratory viruses identified in 72% of pediatric CAP cases 2
• Viral pneumonia typically presents with gradual onset over several days and wheezing, which is a key distinguishing feature—if wheeze is present in a preschool child, primary bacterial pneumonia is unlikely 3, 1
• Children younger than 2 years have viral etiologies documented in up to 80% of cases 1

Atypical Bacterial Pneumonia

• Mycoplasma pneumoniae is identified in 3-23% of cases and is most prevalent in older children and adolescents (5-16 years) 1, 2
• Mycoplasma presents with a slowly progressive course over 3-5 days and a characteristic triad of malaise, sore throat, and low-grade fever 1
• Chlamydophila pneumoniae is more common in infants than older children 1

Other Bacterial Pneumonias

• Staphylococcus aureus (both methicillin-susceptible and methicillin-resistant strains) can cause severe pneumonia with complications including necrotizing pneumonia and empyema 3, 4
• Haemophilus influenzae remains a consideration, particularly in unimmunized or incompletely immunized children 5
• Mycobacterium tuberculosis should be considered, as it was diagnosed in 2.3% of children with CAP in one large cohort 2

COVID-19

• SARS-CoV-2 infection presents with fever, cough, fatigue, nasal congestion, and in severe cases, dyspnoea and respiratory failure 3
• In pediatric patients, COVID-19 may include diarrhea, headache, and poor feeding, with progression to respiratory failure and metabolic acidosis in severe cases 3

Non-Infectious Differential Diagnoses

Malignant Diseases

• Pulmonary malignancies or metastatic disease can present with fever, respiratory symptoms, and radiographic infiltrates that mimic pneumonia 6
• Follow-up chest radiographs at 4-6 weeks should be obtained in patients with recurrent pneumonia in the same lobe or lobar collapse with suspicion of chest mass 3

Interstitial Lung Diseases

• Chronic interstitial lung diseases can present acutely and may be difficult to distinguish from infectious pneumonia without detailed history and follow-up imaging 6

Pulmonary Edema

• Cardiogenic or non-cardiogenic pulmonary edema can present with respiratory distress, tachypnea, and bilateral infiltrates on chest radiography 6

Pulmonary Hemorrhage

• Alveolar hemorrhage from various causes (vasculitis, coagulopathy, trauma) can mimic pneumonia radiographically 6

Foreign Body Aspiration

• Aspirated foreign body should be suspected in children with sudden onset of respiratory symptoms, particularly with unilateral findings or lobar collapse 3
• Follow-up radiographs should be obtained when there is suspicion of anatomic anomaly or foreign body 3

Critical Diagnostic Limitations

A major pitfall in differentiating these conditions is that currently available diagnostic tests have poor discriminatory value:

• Acute-phase reactants (CRP, ESR, procalcitonin) cannot reliably distinguish between viral and bacterial causes as the sole determinant 3, 1, 6
• Chest radiographs cannot reliably distinguish viral from bacterial pneumonia or among different bacterial pathogens 1
• Complete blood count provides limited discriminatory value for differentiating etiologies 3, 1
• The concordance between all available diagnostic tests is low, and there is a high percentage of multiple microorganisms identified even in healthy children 2

Age-Based Approach to Differential Diagnosis

Infants and Children Under 2 Years

• Viral etiologies predominate (up to 80% of cases), with RSV being the most common 1, 2
• Consider bacterial coinfection if there is clinical deterioration, high fever (>38.5°C), or severe disease 1

Children 2-5 Years

• Mixed viral-bacterial infections are common (61% of cases have mixed etiology) 2
• Streptococcus pneumoniae becomes more prevalent as a bacterial cause 1

School-Aged Children and Adolescents (5-16 Years)

• Bacterial pneumonia becomes more common, with Streptococcus pneumoniae as the predominant pathogen 1
• Mycoplasma pneumoniae should be strongly considered in this age group 3, 1

Clinical Features Suggesting Specific Etiologies

Bacterial Pneumonia (Including Pneumococcal)

• Abrupt onset with high fever (>38.5°C) 1
• Absence of wheeze 3
• Severe respiratory distress with oxygen saturation <92% 3

Viral Pneumonia

• Gradual onset over several days 1
• Presence of wheeze 3, 1
• Younger age (<2 years) 1, 2

Mycoplasma Pneumoniae

• Slowly progressive course over 3-5 days 1
• Triad of malaise, sore throat, and low-grade fever 1
• School-aged children or adolescents 3, 1