Most Common Causative Organism of Typical Pneumonia in Children Aged 6-9 Years
Streptococcus pneumoniae (Option C) is the correct answer and the most common causative organism of typical pneumonia in children aged 6 or 9 years. 1
Age-Specific Pathogen Distribution
Streptococcus pneumoniae remains the most common bacterial cause of community-acquired pneumonia across all pediatric age groups, including school-aged children. 1, 2 The British Thoracic Society guidelines explicitly state this as a key point, emphasizing that the incidence of S. pneumoniae is less influenced by age compared to other pathogens. 1
Why the Other Options Are Incorrect:
Respiratory syncytial virus (Option A) is predominantly found in younger children, particularly those under 2 years of age, not in the 6-9 year age group. 1, 3 While viruses account for 14-35% of childhood CAP overall, RSV specifically targets infants and toddlers. 1, 2
Group B Streptococcus (Option B) is a neonatal pathogen causing early-onset sepsis and pneumonia in the first days to weeks of life, and is not a typical cause of community-acquired pneumonia in school-aged children. 4
Clinical Context for This Age Group
In children aged 6-9 years presenting with typical pneumonia (characterized by lobar consolidation, productive cough, and acute onset):
S. pneumoniae accounts for 16-37% of cases when serological testing is used, though blood cultures are positive in only 5-10% of cases. 1
Mycoplasma pneumoniae becomes increasingly common in children over 5 years (accounting for 4-39% of cases), but this typically presents as atypical pneumonia with gradual onset, nonproductive cough, and bilateral interstitial infiltrates—not the typical pneumonia pattern described in the question. 1, 5
Chlamydia pneumoniae is responsible for 0-20% of cases in older children but also presents as atypical pneumonia. 1
Important Clinical Pitfall
Do not confuse the overall epidemiology of CAP with the specific presentation of "typical pneumonia." While atypical organisms like Mycoplasma become more prevalent in school-aged children, the question specifically asks about typical pneumonia, which by definition points to S. pneumoniae as the causative organism. 4, 6 Typical bacterial pneumonia is characterized by lobar consolidation, air bronchograms on chest X-ray, and acute presentation with high fever—all hallmarks of pneumococcal infection. 4
Mixed viral-bacterial infections occur in 8-40% of cases, so co-infection is possible, but S. pneumoniae remains the primary bacterial pathogen to consider. 1, 2, 5