Neonates (<4 weeks): Group B streptococci, E coli

Children (4 weeks-18 years): RSV, Mycoplasma, C trachomatis (infants-3 years), C pneumoniae (school-aged children), S pneumoniae

Adults (18-40 years): Mycoplasma, C pneumoniae, S pneumoniae, viruses (eg, influenza)

Adults (40-65 years): S pneumoniae, H influenzae, anaerobes, viruses, Mycoplasma

Elderly: S pneumoniae, influenza virus, anaerobes, H influenzae, gram Θ rods