Etiology of Pediatric Pneumonia by Age Group
Understanding age-based etiology is critical for empirical antibiotic selection in pediatric pneumonia.
Neonates (<2 months)
Organism Notes E. coli Most common Gram-negative Klebsiella pneumoniae Gram-negative; associated with pneumatoceles S. aureus (Staphylococcus) Gram-positive; causes severe disease Pneumococci Gram-positive Group B Streptococcus (GBS) Common in West; uncommon in India Viral / Fungal Occasional (CMV, Candida in immunocompromised) Aspiration Common cause in neonatal period
India note: GBS pneumonia is uncommon in India unlike Western countries.
Infants 3 months – 3 years
Organism Notes Streptococcus pneumoniae Most common bacterial agent H. influenzae Nearly always associated with bacteremia; age 3m–3y Staphylococcus aureus Causes severe disease; pneumatoceles pathognomonic RSV Chief viral cause under 6 months Parainfluenza, adenovirus Other viral causes
Children >3 years
Organism Notes Streptococcus pneumoniae Still most common Staphylococcus aureus Less common but severe Mycoplasma pneumoniae Atypical; uncommon <4 years Chlamydia pneumoniae Atypical; adolescents Legionella spp. Rare
Atypical Pneumonia Organisms
Organism Age Transmission Mycoplasma pneumoniae School age / adolescents Droplet; winter epidemics Chlamydia pneumoniae Older children / adolescents Droplet Chlamydia trachomatis Young infants (1–3 months) Vertical (birth canal) Legionella Any age (rare) Water source
Mycoplasma is uncommon below 4 years; subclinical infections do occur.
Special Host Situations
Host Likely Organisms Immunocompromised Pneumocystis jirovecii, Histoplasma, Gram-negatives, Staph Severe malnutrition Gram-negative organisms Early infancy Gram-negative organisms predominate Cystic fibrosis Pseudomonas aeruginosa (recurrent exacerbations) Post-measles / post-influenza Staphylococcal superinfection
Overall Etiology Distribution
Viral etiology: ~40% (RSV, influenza, parainfluenza, adenovirus)
Bacterial etiology: >60%
Unknown: ~1/3 of cases
In developing countries (India), bacterial LRTI accounts for 50–60% of cases; common bacteria are sensitive to amoxicillin and cotrimoxazole (WHO ARI program basis).
